Break MessageView into 2 separate activities.

MessageView for regular messages and MessageFileView for EML files.

I'll break down MessageViewFragment too.

Change-Id: Iae66f33d8fb5de58084ab4aef31588e9743c5a18
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index dc5437b..1f7f8ab 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -206,6 +206,10 @@
         <activity
             android:name=".activity.MessageView"
             android:theme="@android:style/Theme.NoTitleBar" >
+        </activity>
+        <activity
+            android:name=".activity.MessageFileView"
+            android:theme="@android:style/Theme.NoTitleBar" >
             <intent-filter android:label="@string/app_name">
                 <action android:name="android.intent.action.VIEW" />
                 <data android:mimeType="application/eml" />