Fix the send button's touch highlight color

Introduce a generic touch highlight background drawable, and use the
proper shades of blue (and gray on v19+).
Use the touch highlight background for the emoji toggle
Add touch highlight to contact photos
Use unified touch highlight in import & export
Replace the attachment dialog header icon with something modern
End conversation selection action mode if all deselected

This seems to be common convention in most apps.
Add missing spaces
Merge pull request #648 from veeti/tweaks-and-polish

Assorted tweaks and polish