#312 - Added a simple method to remotely turn on & off email support

Uses http://api.wordpress.org/iphoneapp/feedback-check/1.0/ to determine if feedback is turned on or off.
#312 - Turn feedback on by default if problems happen when checking
#312 - Eliminated use of obscure ternary operation for nil check
#312 - Replaced instance variable with property for better scoping
Merge pull request #337 from wordpress-mobile/issues/312

#312 - Added a simple method to remotely turn on & off email support