Notifications now check to see the thread they are supposed to open
exists.
Also, clean up FocusedContentStore._onFocus so that it doesn't have the side
effect of dispatching another action and messay logic.
Instead, added Actions.ensureCategoryFocused, to focus any category, and which
should be used separately from focusing content (notifications now use
this action for "opening" the thread)
Also, convert FocusedPerspectiveStore to ES6
- When accounts changed and the saved perspective could reference
accounts that no longer exist and cause all sorts of errors. This is
fixed.
- Add specs
- Fixes some sentry errors
