Replace options menu with action bar

As discussed on the mailing list, this change replaces the action bar dummy on v11+ and the options menu on v7-v10 with a real action bar. This will allow us to implement features such as [navigation drawers](https://developer.android.com/design/patterns/navigation-drawer.html), [search action views](https://developer.android.com/guide/topics/ui/actionbar.html#ActionView), and [spinners in the action bar](https://developer.android.com/guide/topics/ui/controls/spinner.html) more easily and across devices.

This change also includes the v7 appcompat library, its resources, and an updated v4 appcompat library to support the action bar and other new Android features on legacy devices. Unfortunately, the v7 requires a minimum Android version of 7, therefore I raised `android:minSdkVersion`. This was recently discussed on the mailing list as well to better support split views.

**Please reimport the project in Eclipse so that it picks up the appcompat library.** I'm sorry for that, but it seems to be a problem with Eclipse...