Make preference say "today" and "yesterday"

The app preference would say 0 days ago and 1 day ago when
appropriate and we decided that was a little weird. This
changes the behavior to make it say "today" and "yesterday"
in those cases when appropriate since they sound nicer.

Test: Robotests
Bug: 36900272
Change-Id: I0766bbb52fc5d1dba24edf204ee7d66ee10a3888
2 files changed