Update target and support libs to SDK 21, fixing compile issues

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/service/PassphraseCacheService.java

@@ -456,7 +456,7 @@ public class PassphraseCacheService extends Service {
             Intent intent = new Intent(getApplicationContext(), PassphraseCacheService.class);
             intent.setAction(ACTION_PASSPHRASE_CACHE_CLEAR);
             builder.addAction(
-                    R.drawable.abc_ic_clear_normal,
+                    R.drawable.abc_ic_clear_mtrl_alpha,
                     getString(R.string.passp_cache_notif_clear),
                     PendingIntent.getService(
                             getApplicationContext(),

OpenKeychain/src/main/res/layout/actionbar_custom_view_done.xml

@@ -19,7 +19,6 @@
     android:layout_height="match_parent"
     android:dividerPadding="12dp"
     android:orientation="horizontal"
-    android:divider="@drawable/abc_list_divider_holo_light"
     android:showDividers="end" >
 
     <include layout="@layout/actionbar_include_done_button" />

OpenKeychain/src/main/res/layout/actionbar_custom_view_done_cancel.xml

@@ -18,7 +18,6 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:dividerPadding="12dp"
-    android:divider="@drawable/abc_list_divider_holo_light"
     android:orientation="horizontal"
     android:showDividers="middle">