add android-support-v7-appcompat to use ActionBar in Android 2.3

ActionBar is added in Android 3.0, to use it in Android 2.3, we can use support library v7, and use `import android.support.v7.app.ActionBar;` in code.

support library configuration tutorial: https://developer.android.com/tools/support-library/setup.html#libs-with-res