Return RACSignal when building app configuration
Explicitly import RxCocoa in ThingsHubApplication
Implement new RxCocoa flow through app controller

This won't build right now, since I need to add an interface and stub for some of the sync delegate stuff.
Add stub sync delegate interfaces
Add note about sync idempotence to README
[style] Clean up imports across app
Fix app exit code logic

We now use +merge to create a single exit code from several other signals: three which are created on catching an error from the config, auth, or sync signals; and one which returns 0 on completion of the sync signal.

Not 100% sure if this is right, and I bet @andrewsardone can make it cleaner, even if this is correct.
Merge branch 'master' into cdz/app-flow

Conflicts:
	README.md
Update sync method docs in IssueSyncEngine
Fix return code logic: we need to ignore values when computing exit code
Attach status message side effects to their signals
Check types returned from signals
Stub out sync engine with some temporary testing code
Properly flatten the auth client signal when mapping it from the config signal
Use -flattenMap when creating sync engine signal
Print milestones via sync engine

(as proof that the architecture here works)
Add stub ThingsSyncDelegate
Merge pull request #2 from cdzombak/cdz/app-flow

Use RAC for application logic flow