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
