Mms: Add close button for removing subject as a new UX path instead of relying on the depracated onKeyListener

- Vector FTW

Change-Id: I69b1b95cd01f38d3801e33eff6a3dd9c4941fab6
Merge branch 'cm-12.0' of https://github.com/CyanogenMod/android_packages_apps_Mms-caf into cm-12.0