Move upsync from EasMailboxSyncHandler to EasSync.

Eventually EasSync should handle downsync as well, but the immediate
task is to decouple upsync from downsync in EasMailboxSyncHandler.
This move also fixes some upsync bugs.

Also put EmailSyncParser in its own file.

Bug: 10678136
Change-Id: Ie5e131a3f316176c203d275df35d3e8a8f9141c7
5 files changed