[SIP-3] Scheduled email reports for Slices / Dashboards (#5294)

* [scheduled reports] Add support for scheduled reports

* Scheduled email reports for slice and dashboard visualization
  (attachment or inline)
* Scheduled email reports for slice data (CSV attachment on inline table)
* Each schedule has a list of recipients (all of them can receive a single mail,
  or separate mails)
* All outgoing mails can have a mandatory bcc - for audit purposes.
* Each dashboard/slice can have multiple schedules.

In addition, this PR also makes a few minor improvements to the celery
infrastructure.
* Create a common celery app
* Added more celery annotations for the tasks
* Introduced celery beat
* Update docs about concurrency / pools

* [scheduled reports] - Debug mode for scheduled emails

* [scheduled reports] - Ability to send test mails

* [scheduled reports] - Test email functionality - minor improvements

* [scheduled reports] - Rebase with master. Minor fixes

* [scheduled reports] - Add warning messages

* [scheduled reports] - flake8

* [scheduled reports] - fix rebase

* [scheduled reports] - fix rebase

* [scheduled reports] - fix flake8

* [scheduled reports] Rebase in prep for merge

* Fixed alembic tree after rebase
* Updated requirements to latest version of packages (and tested)
* Removed py2 stuff

* [scheduled reports] - fix flake8

* [scheduled reports] - address review comments

* [scheduled reports] - rebase with master

superset/utils/core.py

@@ -4,6 +4,7 @@ from builtins import object
 from datetime import date, datetime, time, timedelta
 import decimal
 from email.mime.application import MIMEApplication
+from email.mime.image import MIMEImage
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
 from email.utils import formatdate
@@ -582,21 +583,23 @@ def notify_user_about_perm_udate(
                     dryrun=not config.get('EMAIL_NOTIFICATIONS'))
 
 
-def send_email_smtp(to, subject, html_content, config, files=None,
-                    dryrun=False, cc=None, bcc=None, mime_subtype='mixed'):
+def send_email_smtp(to, subject, html_content, config,
+                    files=None, data=None, images=None, dryrun=False,
+                    cc=None, bcc=None, mime_subtype='mixed'):
     """
     Send an email with html content, eg:
     send_email_smtp(
         'test@example.com', 'foo', '<b>Foo</b> bar',['/dev/null'], dryrun=True)
     """
     smtp_mail_from = config.get('SMTP_MAIL_FROM')
-
     to = get_email_address_list(to)
 
     msg = MIMEMultipart(mime_subtype)
     msg['Subject'] = subject
     msg['From'] = smtp_mail_from
     msg['To'] = ', '.join(to)
+    msg.preamble = 'This is a multi-part message in MIME format.'
+
     recipients = to
     if cc:
         cc = get_email_address_list(cc)
@@ -612,6 +615,7 @@ def send_email_smtp(to, subject, html_content, config, files=None,
     mime_text = MIMEText(html_content, 'html')
     msg.attach(mime_text)
 
+    # Attach files by reading them from disk
     for fname in files or []:
         basename = os.path.basename(fname)
         with open(fname, 'rb') as f:
@@ -621,6 +625,23 @@ def send_email_smtp(to, subject, html_content, config, files=None,
                     Content_Disposition="attachment; filename='%s'" % basename,
                     Name=basename))
 
+    # Attach any files passed directly
+    for name, body in (data or {}).items():
+        msg.attach(
+            MIMEApplication(
+                body,
+                Content_Disposition="attachment; filename='%s'" % name,
+                Name=name,
+            ))
+
+    # Attach any inline images, which may be required for display in
+    # HTML content (inline)
+    for msgid, body in (images or {}).items():
+        image = MIMEImage(body)
+        image.add_header('Content-ID', '<%s>' % msgid)
+        image.add_header('Content-Disposition', 'inline')
+        msg.attach(image)
+
     send_MIME_email(smtp_mail_from, recipients, msg, config, dryrun=dryrun)
 
 
@@ -639,7 +660,7 @@ def send_MIME_email(e_from, e_to, mime_msg, config, dryrun=False):
             s.starttls()
         if SMTP_USER and SMTP_PASSWORD:
             s.login(SMTP_USER, SMTP_PASSWORD)
-        logging.info('Sent an alert email to ' + str(e_to))
+        logging.info('Sent an email to ' + str(e_to))
         s.sendmail(e_from, e_to, mime_msg.as_string())
         s.quit()
     else:
@@ -651,11 +672,13 @@ def get_email_address_list(address_string):
     if isinstance(address_string, basestring):
         if ',' in address_string:
             address_string = address_string.split(',')
+        elif '\n' in address_string:
+            address_string = address_string.split('\n')
         elif ';' in address_string:
             address_string = address_string.split(';')
         else:
             address_string = [address_string]
-    return address_string
+    return [x.strip() for x in address_string if x.strip()]
 
 
 def choicify(values):