AccountService: Implements default account failsafe
AccountService: Fixes failsafe logic
AccountService: Updating default account fix. II
AccountService: Wiring WPAnalytics for account fix
Adding mixpanel tracking for 4.5 migration fix.

Added code to WPAnalyticsTrackerMixpanel and also pulled in a new version of the stat with a better name.
AccountService: Implements fix unit tests. Updates sort code
Merging latest failsafe branch changes
Adds AccountServiceTests to UnitTests target
Added model version 22 to include Account.uuid
AccountServiceTests: Updated migration fix test
AccountService: Default Account fix should check for token length
ReaderPostsViewController: Prevents Unit Test crash due to nil topic
Merge branch 'issue/2637-implements-default-account-failsafe' of https://github.com/wordpress-mobile/WordPress-iOS into issue/2637-implements-default-account-failsafe
Adds UUID to WPAccount and migration policy to populate
Merge branch 'issue/2637-implements-default-account-failsafe' of github.com:wordpress-mobile/WordPress-iOS into issue/2637-implements-default-account-failsafe
Run fix after entity migration is done
Fixes AccountService Unit Tests
Fixed class name to account for Swift module prefix
Fixes optionals bug in AccountToAccount Migration
Updates Account Migration