Exit most activities when accounts are deleted

This resolves cases like this:  You are in the inbox of an Exchange
account.  You click home, settings, accounts & sync, and you delete
the account.  Now re-enter the Email app.  You'll be left in a strangely
empty inbox, for an account that no longer exists.

* Set a flag any time the reconciler deletes an account
* Check that flag in onResume of any activity that depends on the account
    list and could be left in an "empty" state if account(s) are deleted.
* The Activities in which we check it are:
  * AccountFolderList
  * AccountSettings
  * MailboxList
  * MessageCompose
  * MessageList
  * MessageView
* Clear the flag any time we come in through Welcome, which will dispatch
    to other activities properly based on the number of accounts found.

Bug: 2563998
Change-Id: I00fc542581c2bed92d744a4c2e48a88f83737f11
1 file changed