Only reschedule polling and setup pushing when necessary due to
particular setting changes. Makes the K-9 Mail UI much more
responsive to setting changes that do not affect polling and pushing.
The poll schedule is deliberately only rescheduled when the period is
decreased. An increase in period will still allow the next scheduled
check to happen as originally scheduled.
* Add an explicit configuration option for stars
* Replace now-outdated "left handed" widgets config option, now that
select widgets are always on the left.
* since the multi-modality of the message list was now only a "toggle
stars" option, kill that, as it was lots of code and rather redundant
global config option rather than a per-account one. (But with a new
implementation.) - As we now have views that show messages across
accounts, this needed to become a global)
