Merge pull request #245 from m0vie/fixes

fixes for split-view changes
changelog update
Bumped manifest to 4.323
Simplify and improve message view header layout.

The star was displayed partially off-screen before.
Simplify message list item layout.
Fix typo in changelog
Another unused import.
Swap previous and next buttons in MessageViewFragment.

Makes sure to keep behaviour consistent with previous versions.
Make next/prev buttons track their state again.
Tweak animations to use the (Slightly slower) android default animation speed.
Remove the fadeout to make things look a little less weird
Make the animations slide in from the edge. (See the aforementioned comment about jankyness)

TODO: don't remove the message view until _after_ the animation runs. Before HC, that requires rather a lot more code (writing a whole animationadapter) than it should.

TODO: get the messageview to stop jumping to hide the header area as it's displayed.
Only animate the firt view transition if it's from the message list to the message view
Because we're not reusing the message view, we don't need to force scrolling. This has the side effect of cutting down on a momentary flash of message header area on display.
MessageView: another theme fix

- The attachments view still had the wrong background color in case
  of different global and message themes.

- The attachments view used the activity LayoutInflater, but it needs
  to use the one of the fragment.

- The background drawable for the attachments used transparency, and
  thus was completely invisible in the black theme. Fix it by adding
  another one for the black theme.
Fix NullPointerException when message list hasn't loaded

This may happen on menu -> switch to (light/dark) theme, because
then the whole activity is restarted