Add test to detect failure in snapshot API

Currently, there is at least one bug with snapshot API, but
tests are not detecting. This adds a test to detect when event
overlay is present in a snapshot.
Fix bug in requesting event query on snapshots and 2 other things

1. Fix bug in building the request to snapshot without events (Fixes #99)
2. Remove commented code
3. Add .idea to .gitignore
Assert event_query is not in the response and output response as assertion message
Use Pillow instead of pil
Clean up requirements code in setup.py
Merge pull request #104 from DataDog/isaac/snapshot_api

Fixes #99 and improves testing.
Revert "Merge pull request #104 from DataDog/isaac/snapshot_api"

This reverts commit b261bb86b29482c706e77b5f59b13de11c696474, reversing
changes made to 0cb1bac1ad92982ed88932014c104b51f8c0bdf0.
Revert "Revert "Merge pull request #104 from DataDog/isaac/snapshot_api""

This reverts commit 6fd4526da94ba1f7b04a38b2050908a45249d1c9.
Bump version to 1.9.1 and update change log
Test dashboard creation validation #25 and #26
Add command option to get dog version #65
Correct examples in docstring #100
Merge pull request #108 from DataDog/isaac/bug_fixes

Isaac/bug fixes
Add optional graph_def parameter #78

Allows user to enter the graph definition instead of simply using
the metric query. This will make it possible to obtain snapshots
of any query and visual type.
Refactor snapshot from graph_def into a new method
snapshot_ready method to snapshot API and fix failing integration tests
Make handle optional for commenting and fix failing integration test #29
Undo changes that break backward compatibility
Import from urllib.parse in python 3
Update docstring and refactor http request call parameters