Refactor browse command to draw data from central model in httprequests.lua
add proper URI created by VLC's make_uri command to attributes in the browse data.
(this means that clients can simply use the correct URI for browse,open,enqueue commands,
rather than trying to convert paths to URI) accept file uri as input for browse command
(so that clients can completely ignore the path attribute) browse.xml displays data from
the model (fully backward compatible) browse.json provides alternative view of the same data