Increase parity between api search and on-wiki search

Increase parity between api search and on-wiki search

The on wiki search indicates more information than is currently
available by api.  Adds two more props to improve parity:

* categorysnippet: similar to the other snippets, about the category
  that triggered the match
* isfilematch: indicates if the match was part of file content

Additionally when 'suggestion' is included as part of the searchinfo,
'suggestionsnippet' is now also returned.

Change-Id: Ibf18905775a79caed213aca1bdebcffe3644c23b