Rename panic button in framework settings.

Renamed panic to "emergency" or "emergency gesture" to
avoid speculation once source code is accessible to
parties without full context.

The settings string and file names still use the word "panic". This
will be updated in a follow-up CL

Bug: 169946710
Test: rebuild
Change-Id: Ic1a3181145ca2b64ab6ef2a2989224395fa9a6f8