Fix for not listing subcategories download plugin

Not listing subcategories when you don't have them on main page
(unchecked in preferencies)
Found while working on #479.  Related with  #566. Probably only mistake.
Fix fatal error in menu manager when using SetEnv E_DEV_MEN
Fixes #548
Typo in last commit, whoops. (#548)
Merge pull request #573 from Jimmi08/download-subcategories

Fix for not listing subcategories download plugin
Fixes #514 - _blank theme config
Fixes #547 - PM plugin issuse (outbox messages not rendering, outbox count, and outbox date)