Upgrade support library. Switch gradle build tools and AS to 2.0. Adapt code to new support lib

app/src/main/res/drawable/ic_reader_background_checkbox_black_24dp.xml

@@ -1,9 +0,0 @@
-<vector xmlns:android="http://schemas.android.com/apk/res/android"
-        android:width="24dp"
-        android:height="24dp"
-        android:viewportWidth="24.0"
-        android:viewportHeight="24.0">
-    <path
-        android:fillColor="#FF000000"
-        android:pathData="M19,3H5C3.9,3,3,3.9,3,5v14c0,1.1,0.9,2,2,2h14c1.1,0,2-0.9,2-2V5C21,3.9,20.1,3,19,3z"/>
-</vector>

app/src/main/res/drawable/ic_reader_background_checkbox_white_24dp.xml

@@ -1,9 +0,0 @@
-<vector xmlns:android="http://schemas.android.com/apk/res/android"
-        android:width="24dp"
-        android:height="24dp"
-        android:viewportWidth="24.0"
-        android:viewportHeight="24.0">
-    <path
-        android:fillColor="#FFFFFFFF"
-        android:pathData="M19,3H5C3.9,3,3,3.9,3,5v14c0,1.1,0.9,2,2,2h14c1.1,0,2-0.9,2-2V5C21,3.9,20.1,3,19,3z"/>
-</vector>

app/src/main/res/drawable/reader_background_checkbox.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
-    <item android:state_checked="true" android:drawable="@drawable/ic_reader_background_checkbox_black_24dp" />
-    <item android:drawable="@drawable/ic_reader_background_checkbox_white_24dp" />
+    <item android:state_checked="true" android:drawable="@drawable/reader_background_checkbox_selected" />
+    <item android:drawable="@drawable/reader_background_checkbox_unselected" />
 </selector>

app/src/main/res/layout/reader_popup.xml

@@ -39,10 +39,6 @@
         android:layout_width="wrap_content"
         android:layout_height="36dp"
         android:gravity="center"
-        android:paddingLeft="4dp"
-        android:paddingRight="4dp"
-        android:layout_marginLeft="4dp"
-        android:layout_marginStart="4dp"
         android:text="@string/pref_reader_theme"/>
 
     <android.support.v7.widget.AppCompatCheckBox