Added code to support a cache option for filebrowser widget.

This new option will allow code that uses the filebrowser to specify
whether or not to cache files read from the server when clicking on
a path.  If not using cache, files will be re-read from the server.

Change-Id: Ife4cc398d8589345b61f044b4a855d4246f54b5a
Merge topic 'pvweb-add-filebrowser-cache-option-rel' into master

59ae032d Added code to support a cache option for filebrowser widget.