Don't stack toasts for every user press

Showing a toast on every press was adding up to a long list of
toasts to clear out of the display, now cancel the last so we
don't have that problem.

Also fix unlock strings to not use insertions because of problems
translating the context.

Bug: 16892731
Bug: 16366701
Change-Id: Ia523469089c9f8dd1f3e466a9d4ea901a376d1bc