ADD: [plexbmc] single "section..." entry

Single section... entry for menus with no categories.  Need to use the
"nocat" options on the runscript for the skin.
ADD: [plexbmc] a refresh entry

Allows cache to be recreated if new media servers comes along
Merge pull request #1 from hippojay/plexbmc-sections

Plexbmc sections update by Hippojay