Messaging: Remove duplicate code

* mmslib contains basically the same code as android.support.v7.mms.pdu
  does, so align them code-wise and remove the mmslib duplicates
* Since mmslib contains a few usages that are now not accessible
  anymore, make the classes or methods public where it complains

Change-Id: I10b8716c0e45079e4795fda4489dc1a9535026f3

src/com/android/messaging/util/FileUtil.java

@@ -22,6 +22,7 @@ import android.content.Context;
 import android.net.Uri;
 import android.os.Environment;
 import android.os.ParcelFileDescriptor;
+import android.support.v7.mms.pdu.ContentType;
 
 import com.android.messaging.Factory;
 import com.android.messaging.R;