Fix several folder picker bugs

* Fix a crash when the folder picker is loaded and the SDK becomes
  authorized outside of the folder picker due to view hierarchy
  inconsistencies. Fixes GH-44.
* Reset folder picker navigation title to nil when presenting the
  authorization webview.
* Ignore BoxSDKOAuth2ErrorAccessTokenExpired in error handler. This
  error code indicates the SDK is attempting an automatic refresh.
  It does not indicate a logged out state.
* Fix bug where navigation bar loses styling when the folder picker
  is dismissed and represented.
Kill ODRefreshControl and listen to notifications from the SDK only when appropriate in folder picker
Merge branch 'folder-picker-bugs'

Conflicts:
	BoxSDK.xcodeproj/project.pbxproj