Update android support library to latest version.
Remove own Notification.Builder abstraction.

Replace it by NotificationCompat.Builder, which is in the support
library we're using anyway.
First stab at new notifications.
Add actions to notifications.

- If there's only a single message in the notification, add 'Reply' and
  'Read' (marks as read) buttons.
- If there's more than one message pending, add only 'Read'.
Add German translation for new strings.
Fix marking messages as read from notification.

MessagingController.setFlag(Account, List<Long>, Flag, boolean, boolean)
expects database IDs, while Message.getId() returns UIDs. Fix the
operation by using a variant that expects UIDs.
Respect "Show contact names" option when determining sender for
notification.

Fixes #4765.
Simplify code and beautify pre-jellybean notifications by using bold
sender span for those.
Fixed deprecation warnings.
Update summarized notification if a message is deleted or read remotely.
Add delete action to notification.
Add German translation for message delete notification action.
Some fixes to notification behaviour.

- Make notification high priority if any previewed message is flagged
- Fix message ordering
- Go to folder list instead of folder of newest message if there are
  multiple messages in the notification
Incorporate review comments.
Fix message overflow.
Directly go to message when clicking on a single-message notification.
Cancel notification when viewing message by clicking on notification.
In the new-style notification, directly go to message if new message
count is 1.

This matches what is displayed in the notification itself.
Reset list of unseen messages when the user clears the notification.
Strip off signatures from preview.