Add Lollipop lock screen notifications.

Add vector versions for some notification icons (yay Illustrator)
Add comments reminding people to add their settings to GlobalSettings.
<plurals> support for notification_new_messages_title
Not sure why #ffffffff is resulting in black with targetSdk 17.
Merge pull request #512 from k9mail/lollipop_lock_screen_notifications

Lollipop lock screen notifications
Oops, checking wrong platform capability.
Merge remote-tracking branch 'upstream/master'