Cleanups
Followup: Use the right Suggestion model
Remove pootle_app.Suggestion model

remove from_suggestion field from Submission model
(last part of evernote/pootle#163)

Pick notes: Adjusted the migrations to match our numbering and our models.
    Did other minor changes due to code divergence.

Conflicts:
	pootle/apps/pootle_app/models/__init__.py
	pootle/apps/pootle_app/models/suggestion.py
	pootle/apps/pootle_statistics/models.py