Skeleton for remote query execution using celery. (#908)

* Carapal react mockup

This is really just a mock up written in React to try different
components. It could become scaffolding to build a prototype, or not.

* Preliminary commit for Celery backend

* Move the SQL query execution to the celery worker.

* React scetch

* Refactor SQL execution to use the celery if configured.

* Refactor SQL execution to use the celery if configured.

* Add query model

* Remove QueryResult. Query has a tmp_table_name field that has all the data.

* Add create table as wrapper.

* Create table as

* Address the comments.

* Add trailing commas

* Remove the init_query test.

* Handle 'undefined' schema case

setup.py

@@ -16,6 +16,7 @@ setup(
     zip_safe=False,
     scripts=['caravel/bin/caravel'],
     install_requires=[
+        'celery==3.1.23',
         'cryptography==1.4',
         'flask-appbuilder==1.8.1',
         'flask-cache==0.13.1',