ThemePicker: "Apply theme" initial implementation

Use the current API to apply the packages for a given theme.
Still pending is storing the applied overlay packages, and applying the
default theme.

Bug: 120559294

Change-Id: I7c15f8ab94b1dec8576141eaecd4f3e059249fb1
diff --git a/res/layout/fragment_theme_picker.xml b/res/layout/fragment_theme_picker.xml
index 0fd4044..ef40334 100644
--- a/res/layout/fragment_theme_picker.xml
+++ b/res/layout/fragment_theme_picker.xml
@@ -46,6 +46,7 @@
             android:layout_width="match_parent"
             android:layout_height="wrap_content">
             <Button
+                android:id="@+id/apply_button"
                 style="@style/ActionPrimaryButton"
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
diff --git a/res/values/strings.xml b/res/values/strings.xml
index d87a354..7d94334 100755
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -65,4 +65,7 @@
 
     <!--Title for a grid option, describing the number of columns and rows, eg: 4x4 [CHAR LIMIT=10] -->
     <string name="grid_title_pattern"><xliff:g name="num_cols" example="1">%1$d</xliff:g>x<xliff:g name="num_rows" example="1">%2$d</xliff:g></string>
+
+    <!-- Message shown when a theme has been applied successfully in the system [CHAR LIMIT=NONE] -->
+    <string name="applied_theme_msg">Theme has been applied</string>
 </resources>