Multiple changes to address common errors

1) Adds a fallback when using the iOS Simulator to ensure that local
account status is properly returned
2) Collects error checking to all reside before the user can click the
button to initiate the request
3) Removes excess NSAsserts. We're all adults here.
Modernizes project and sample for iOS6 / iOS7.

Removes old, unnecessary kludges required for targeting
Twitter.framework and Social.framework which were required for iOS5
support. Also updates TWSignedRequest to make synchronous call the way
that one should with iOS6+ support.

tl;dr no more iOS5 makes everything better
Removes assert that was failing on GET requests.

Resolves #11.
At some point I guess I should heed my own warnings.
Merge branch 'master' of github.com:seancook/TWReverseAuthExample

Conflicts:
	Source/Classes/TWAPIManager.m