Save the focused conversation via id instead of position

Don't rely on saving the position in the adapter because the position
might change as the adapter's data set changes (e.g. new mails via sync),
and we have no way of modifying the focused position accordingly.

Instead, save the focused conversation with its id (tried using the uri,
but the uri might change when the conversation gets cached). This way,
no matter what happens to the items in the adapter, the focused item
remains consistent.

b/18027602

Change-Id: I51aa68bc15c5892c3b34bde5c199de281390ce7b
6 files changed