New design for Conversation Activity.

1) Move to Fragments for the list view.
2) Switch to CursorLoader from my jankey self-managed cursor.
3) Add session security logic to the ActionBar.
4) Fix colors to be less ugly.

res/menu/conversation_button_context.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<menu xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:title="Send unencrypted"
+          android:id="@+id/menu_context_send_unencrypted" />
+</menu>