Shorten title name so as not to hit char limit.

This is a follow up CL to my previous CL [1], which tried to rename a
settings item "Add virtual keyboard" but ended up with hitting char
limit in many languages.  We decided to use "Manage keyboards" instead
so as not to hit char limit.

 [1]: Id2ae61519152bbe622aa5915f728a4cbbc49e078
      611410a8

Bug: 27543291
Bug: 27959401
Change-Id: I6e4795f8c4dbe9857d036ca19689e05658aa0640