notifications 6.x-1.0-beta2

Some features/documentation and many bug fixes:
- Hiding sending methods for user pages if only one, by jaydub, #250161
- Spin off notifications_mail2web to it's own package, http://drupal.org/project/mail2web
- Fixed multiple strings across all modules, by rastatt, #290063
- Implemented hook_requirements for checking enabled sending methods
- Fixed node subform parameters in notifications_ui_form_alter
- Fixed typo in notifications_autosubscribe form text
- Added inline documentation about the messaging/notifications API
- Removed obsoleted 'pull' operation in notifications_messaging()
- Better query building and more flexibility in notifications_user_get_subscriptions()