fix(rtl-layout): Mirror arrow buttons in rtl layout

The attribute android:autoMirrored="true" requires API level 19, we therefore
have to create a dedicated layout.

Fixes #657

Author: wdullaer

library/src/main/res/layout-ldrtl/mdtp_daypicker_group.xml

@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="utf-8"?>
+<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent" android:layout_height="match_parent">
+    <ImageButton
+        android:id="@+id/mdtp_previous_month_arrow"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:minWidth="48dp"
+        android:minHeight="48dp"
+        android:src="@drawable/mdtp_ic_chevron_right_black_24dp"
+        android:background="@drawable/mdtp_month_arrow_background"
+        android:visibility="invisible"
+        android:nextFocusForward="@+id/mdtp_next_month_arrow"
+        android:contentDescription="@string/mdtp_previous_month_arrow_description"/>
+    <ImageButton
+        android:id="@+id/mdtp_next_month_arrow"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:minWidth="48dp"
+        android:minHeight="48dp"
+        android:src="@drawable/mdtp_ic_chevron_left_black_24dp"
+        android:background="@drawable/mdtp_month_arrow_background"
+        android:visibility="invisible"
+        android:contentDescription="@string/mdtp_next_month_arrow_description"/>
+</FrameLayout>

sample/src/main/AndroidManifest.xml

@@ -6,7 +6,8 @@
         android:allowBackup="true"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"
-        android:theme="@style/AppTheme" >
+        android:theme="@style/AppTheme"
+        android:supportsRtl="true">
         <activity
             android:name=".MainActivity"
             android:label="@string/title_activity_main" >