1. Generalize the code for the various spinners that control
account check frequency.
2. Provide an API for looking up store attributes (and refactor
existing instatiateStore logic to use it).
3. Cleanup the old code that was used to setup frequency spinners.
4. Hardwire Exchange accounts to default into push mode.
Notes to tester:
1. For each account type (POP, IMAP, EAS) we need to check that
auto & manual creation "do the right thing" for frequencies.
POP & IMAP should offer "none" or time intervals, while EAS
should offer "push", "none", or time intervals.
2. EAS accounts should default to "push", all others to "15 min"
3. Make sure that you can edit existing account settings and see
the right choices (only EAS should be offered push).
4. I couldn't write an automated test for the mail checker service,
please confirm that POP & IMAP accounts are checked at the right
intervals (or never, if set for "none".)
BUG=1776149
Automated import of CL 144953
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
