Bump up minimum supported Android version, add ActionBarSherlock dep.

The minimum supported Android device is now 2.2 (Froyo).
And we're embracing the ActionBarSherlock madness.
Remove deprecated <2.2 caching functionality that breaks modern devices.
Stop showing GPL as a weird EULA.
Remove non-themed theme madness.
Switch to QuickContactBadge.
Restyle conversation list view.

1. New look for quick contact badges.
2. No more unread indicator, replace with bolded text.
3. Style message count with color rather than parens.
4. Remove "New Message" item, add as item in action bar instead.
Move to a Fragment world.

1) Start breaking the UI out into Fragments.
2) Switch to Cursor loaders from managed cursors.
3) Switch to inflated menu resources.
4) Break out some basic functionality into helper classes.
New design for Conversation Activity.

1) Move to Fragments for the list view.
2) Switch to CursorLoader from my jankey self-managed cursor.
3) Add session security logic to the ActionBar.
4) Fix colors to be less ugly.
Update look for RecipientsPanel.

1) Make the "add contacts" graphic more holo-ific.
2) Adjust the graphic position on holo-themed devices.
Suppress soft keyboard on Conversation load.
Update conversation item style.

1) Don't print sender/recipient name in message body.
2) Do the split conversation icon view.
3) Adjust font sizes and colors.
Fix passphrase prompt dialog activity.
Fix the look of tabbed multi-contact selector.

1) Updated to ActionBar style.
2) Split out into fragments.
3) Switch to cursor loaders.
Make the 'up' buttom on ConversationActivity work.
Clean up key/identity verification Activites.

1) Get ride of the crazy button situation.
2) Actionbar-ify and abstract out the common actions.
3) Switch to full activities from dialog themes.
Fix view identity key QR code action.
Fix review identity activity UI.
Switch to Contextual Action Bar goodness.
Update the key exchange icon look.
Updated lock icon image