* Use concrete declarations, not the old sample code
* Remove unused "sample" code
* Create ExchangeSender.java
* Strip out the unused (old sample code) parts of ExchangeStore.java
* Unit test to make sure EAS is being offered
* Fix "account leak" in AccountSettingsTests
This was triggered by donut bug # 2092944 but the solution is
different because we support EAS here.
the shipping client will include the necessary generic pieces for
configuring an Exchange client (e.g. account setup) but will not
include actual Exchange client code (e.g. transport / protocol).
Also added a "sample code" implementation of Exchange for use
as a starting point for implementors. (Note, this will not ship
in Donut, it's a placeholder for working on the "framework"
aspects.)
BUG=1740621,1740626
Automated import of CL 144525
