moved iOS/iPhone EmailComposer plugins to outside repo

Moved 3 iOS/iPhone plugins into a single repo @ https://github.com/steve-jansen/cordova-ios-emailcomposer:
  * iOS/EmailComposer
  * iOS/EmailComposerWithAttachments
  * iPhone/EmailComposer

New features / changes:
  * plugman/cordova-cli support
  * cordova plugin spec 2.x+ implement
  * ARC support
  * improved JS API
  * unit tests
  * and more, see see https://github.com/steve-jansen/cordova-ios-emailcomposer/README.md