Filtering, groups and events: model and saving

Regarding issue https://github.com/getsentry/sentry/issues/1267
Created the eventfiltertagvalue model, and created migration for it.
Saving the new data to database is done in event_manager.py

This is the first draft with just "It runs" tests done to it.
Filtering, groups and events: model and saving

Regarding issue https://github.com/getsentry/sentry/issues/1267
Saving bugs.
Filtering, groups and events: model and saving

Regarding issue https://github.com/getsentry/sentry/issues/1267
Saving bugs.
Filtering, groups and events: model and saving

Regarding issue https://github.com/getsentry/sentry/issues/1267
Recreated Migrations