MMS: Make conversation area theamable
Don't recycle messages by default.

* Don't delete old messages by default.
* If any of the conversation threads have more messages than
  the storage limit settings, an activity is shown that will
  tell the user how to turn on the storage limits.
* This changes the behavior introduced in commit
  f766f33b774cfb6dd4100a6522ffa23c0a0dae35

Change-Id: I7e20ec73fbe42e19397cda2663de7434557f0e51