Add dirty wallets to disc sync schedule.

There were several places where various account files (wallet, tx, or
utxo stores) were being marked as dirty, and then not being either
immediately synced to disk or marked as a dirty account so they would
be scheduled to be synced to disk.  This change adds Account functions
to mark as dirty and add the account to the map of scheduled accounts
so they won't be missed by the disk syncer goroutine.