Use a RecyclerView for the ConversationView and

properly notify the view adapter of dataset changes
in order to avoid invalidating the entire dataset when not absolutely necessary.

This change also shows unread messages in a different color,
so users do not fail to notice delayed messages.

briar-android/res/layout/activity_conversation.xml

@@ -1,12 +1,18 @@
 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout
 	xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:tools="http://schemas.android.com/tools"
 	android:id="@+id/layout"
 	android:orientation="vertical"
 	android:layout_width="match_parent"
 	android:layout_height="match_parent">
 
-	<!-- ListView will get inserted here -->
+	<android.support.v7.widget.RecyclerView
+		android:id="@+id/conversationView"
+		android:layout_width="match_parent"
+		android:layout_height="0dp"
+		android:layout_weight="1"
+		android:scrollbars="vertical"/>
 
 	<ProgressBar
 		android:id="@+id/listLoadingProgressBar"
@@ -15,7 +21,8 @@
 		android:layout_gravity="center"
 		android:gravity="center"
 		android:layout_weight="1"
-		android:indeterminate="true"/>
+		android:indeterminate="true"
+		android:visibility="gone"/>
 
 	<TextView
 		android:id="@+id/emptyView"
@@ -26,7 +33,8 @@
 		android:gravity="center"
 		android:padding="@dimen/margin_large"
 		android:textSize="@dimen/text_size_large"
-		android:text="@string/no_private_messages"/>
+		android:text="@string/no_private_messages"
+		android:visibility="gone"/>
 
 	<View
 		android:layout_width="match_parent"

briar-android/res/layout/list_item_msg_in.xml

@@ -11,6 +11,7 @@
 	android:paddingBottom="@dimen/margin_small">
 
 	<RelativeLayout
+		android:id="@+id/msgLayout"
 		android:layout_width="wrap_content"
 		android:layout_height="wrap_content"
 		android:layout_gravity="left|start"

briar-android/res/layout/list_item_msg_out.xml

@@ -11,6 +11,7 @@
 	android:paddingBottom="@dimen/margin_small">
 
 	<RelativeLayout
+		android:id="@+id/msgLayout"
 		android:layout_width="wrap_content"
 		android:layout_height="wrap_content"
 		android:layout_gravity="right|end"