ConfigActivity: Make the two-pane layout more readable

Highlight the selected configuration, and add a border between the two
panes.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

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

@@ -10,7 +10,8 @@
 
     <ScrollView
         android:layout_width="match_parent"
-        android:layout_height="match_parent">
+        android:layout_height="match_parent"
+        android:background="?android:attr/colorBackground">
 
         <RelativeLayout
             android:layout_width="match_parent"

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

@@ -10,7 +10,8 @@
 
     <ScrollView
         android:layout_width="match_parent"
-        android:layout_height="match_parent">
+        android:layout_height="match_parent"
+        android:background="?android:attr/colorBackground">
 
         <RelativeLayout
             android:layout_width="match_parent"

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

@@ -11,6 +11,7 @@
     <RelativeLayout
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
+        android:background="@drawable/list_item_background_anim"
         android:padding="16dp">
 
         <TextView

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

@@ -2,5 +2,6 @@
 <TextView xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
+    android:background="?android:attr/colorBackground"
     android:gravity="center"
     android:text="@string/placeholder_text" />