Add a My Blogs tab with option to add new blogs

Clicking the plus in the toolbar open the `CreateBlogActivity` which
allows the user to create a new blog. Only the first identity is
considered, but support for more identities can be easily added later.

The actual list of blogs in the My Blogs tab will be done in the next
commit.

briar-android/src/org/briarproject/android/util/AndroidUtils.java

@@ -56,6 +56,11 @@ public class AndroidUtils {
 			til.setError(null);
 	}
 
+	public static void setError(TextInputLayout til, int res,
+			boolean condition) {
+		setError(til, til.getContext().getString(res), condition);
+	}
+
 	public static String getBluetoothAddress(Context ctx,
 			BluetoothAdapter adapter) {
 		// Return the adapter's address if it's valid and not fake