fix missing attribute crash

fixes #3328
fixes #3329
fixes #3330
// FREEBIE

res/layout/message_details_header.xml

@@ -9,7 +9,6 @@
     <FrameLayout android:id="@+id/item_container"
                  android:layout_width="match_parent"
                  android:layout_height="wrap_content"
-                 android:background="?conversation_background"
                  android:paddingTop="15dp"
                  android:paddingBottom="15dp"
                  android:elevation="2dp" />

res/layout/recipient_filter_item.xml

@@ -23,7 +23,7 @@
     android:orientation="vertical"
     android:layout_width="fill_parent"
     android:layout_height="?android:attr/listPreferredItemHeight"
-    android:background="?conversation_background">
+    android:background="?android:windowBackground">
 
     <LinearLayout android:id="@+id/name_and_label"
         android:layout_width="fill_parent"

res/values/attrs.xml

@@ -26,7 +26,6 @@
     <attr name="centered_app_title_color" format="reference|color" />
     <attr name="ic_arrow_forward" format="reference" />
 
-    <attr name="conversation_background" format="reference|color"/>
     <attr name="conversation_editor_background" format="reference|color"/>
     <attr name="conversation_editor_text_color" format="reference|color"/>
     <attr name="conversation_delivery_delivered" format="reference"/>