Mms: Allow text input field to expand upto 6 lines

Change-Id: Ia06f249ca4ad68cf03ff4b41493bc158d5cdc7d7
Mms: Fix inconsistent back button behavior

By default, a press of the back button will only take effect when the
button is successfully released (the user releases the button while
still focused on it), not when the button is still triggered and pressed
down. To avoid this inconsistent behavior, execute the custom back
logic in the onBackPressed callback instead of onKeyDown.

Change-Id: I1446e0d7438e467f2d0d02d18cf8d3c68a4eed90
merge changes from Omni 4.4 into local branch