Adding from __future__ imports (#288)

* Adding from __future__ imports

* fixes

* Fixing doctests

* Removing unused ColorFactory (in js now)

* linting

caravel/data/__init__.py

@@ -1,4 +1,8 @@
 """Loads datasets, dashboards and slices in a new caravel instance"""
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
 
 import gzip
 import json