Separate Multi-part SMS setting from size

This does the foll.:

- Separates the toggle from the size (makes more sense)
- Defaults to true, so users find no diff in behavior
- Default convert value for MMS to 7
  (I would suggest that the sprint devices set it via overlay to -1)
- Generalize numberpicker dialog message

Change-Id: I5b6fb33c3cc56a4078d0170a080ccee840afdbf1
Fix: avoid FC for dirty flasher

due to a boolean/int change dirtyflashe will get massive
fc on settings. Rename used value to avoid this problem

cheers

Change-Id: I0cc6597387b2773957d3986e7f1524b6afb31439