Fix sorting of threaded messages.
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.
Fix a potential NullPointerException when rotating the device twice

When MessageListFragment is on the back stack and the device is rotated
the instance state will be restored but no new view will be created. If
the device is rotated again onSaveInstanceState() is called and we have
to take care not to assume that the views have been created.
Simplify Handler code to restore message list state
Fix restoring instance state of fragment on back stack
Avoid saved state being discarded when message list is modified
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.
MessageView: fix crash when clicking on URLs in WebView

The ContextThemeWrapper added in a74d57cb71d67e42e1db709e00d5fd514b1ecd0c
used getActivity().getApplicationContext() to get the base context.
This is wrong, because an Application context won't work for starting
activities from the WebView.

Instead, use the context that is given to us in the constructor as base
context. This is the one that would also  be used if no ContextThemeWrapper
was present at all.
Remove old subject from action bar when loading new message
Restructure MessageHeader to avoid NPE when used by MessageTitleView
Fix NullPointerException
Don't show animation when directly opening message view