FS#2415, add $INFO to mediamanager

- refactor pageinfo() 
now.  basicinfo() establishes the common $INFO keys, mostly user & permission related.
pageinfo() and mediainfo() add additional keys for page and mediamanager requests

- shift MEDIAMANAGER_STARTED after mediainfo() sets up $INFO, this brings it into line with DOKUWIKI_STARTED.  I shouldn't think this will affect any plugins.