#673 - Added OAuth2 token to API call to verify WP.com connectivity

Updated the app delegate to include the OAuth2 token in the call out to WP.com for verification of credentials.  This is NOT the ultimate solution.  Auth verification should be a function of WPAccount.  Removed the NSUserDefaults for the flag to indicate if the app is authenticated for WP.com - presence of OAuth2 token is the best guess at auth status upon app launch.

Updated minimum WordPress install version to 3.5 per our release notes.

WP.com-centric UI does not handle a revoked OAuth2 token properly (Reader for example)
#673 - Wipe OAuth2 token if check upon launch fails

Should probably be centralized so that any time an API request fails with a fault we tell the user to try logging in again.  Way too many changes for that to be safe in this release.
#673 - Turn WordPressComApi authToken into a real property
Merge pull request #685 from wordpress-mobile/issue/673-fix-checkWPcomAuthentication

#673 - Fix WP.com auth to use OAuth2 token and wipe when fails