Rework service to use provider accounts and controller.

* Rewrite service logic to select and update one account at a time
* Add checkmail API to Controller, and much rework/cleanup of existing
   callback API's
* Rewrite notification posting code
* Rewire connection to MessageList to be opened by notifications, to
   cancel notifications, and to reset the "new message" count whenever
   an account is viewed.
* Boilerplate cleanup to a lot of activities because they share the
   callbacks that have had minor changes.
* Remove old push controls from Store API

In progress:
* To provide notification mechanism for EAS pushed mail
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