refactor and improve contact selection

* unify single and multi contact selection activities
* follow android listview design recommendations more closely
* add contact photos
* change indicator for push to be more obvious
* cache circle-cropped bitmaps
* dedupe numbers when contact has multiple of same phone number
* hide contact sections based on preferences (if you choose not to use TextSecure for outgoing SMS to non-push users, those users will be hidden now)