Add avatars in desktop notifications for comments

This adds avatars for desktop notifications about new comments. It uses
the existing "Hide user avatars" preference, though I could see it
needed as two separate settings...
That's pretty much it. I've been using it for a week and it's pretty
nice :)
Match code style
Version 1.0.30
- Doubled default and minimum refresh periods for both OSX and iOS
- Halved the concurrent request limit for queries
- Made User-Agent more descriptive to allow better monitoring of traffic based on version and OS
temporary
Version 1.0.30 #2
- Corrected comment unread issue
Merge pull request #130 from HouseTrip/team-octopus/temporary

Team Octopus - Comment correction
Merge pull request #129 from Timothee/add-avatar-in-notifications

Add avatar in notifications
Quick for for DB migration and 10.8 compatibility in @Timothee ’s cool feature
Moved comment avatar loading off the main thread and tied it to the image loading layer, added avatars to mentions as well
Small code cleanup
- Event-based API polling of repos, far reduced queries but needs testing
- Improved sync performance
- Slightly reduced level at which user is warned of high API usage
Improved user agent with “dev” and “release” segment
Corrected an over optimisation
App version simplification, added timing check on API calls
- Corrected issue that missed closed/merged PRs
Build bump
Added explicit 304 handling in the API events query
Tweak to error response logging
Slightly clearer sorting options
Version bump for release
Merge pull request #134 from HouseTrip/team-octopus/trailer-event-based-polling

Team Octopus - Trailer 1.0.32