Fix cmus-filter for parens, brackets, and missing files

* Gets full path of files after selection.  Ideally I'd have
  hash[full/path/to/album] = 'album' show album in dmenu while returning
  the hash key, but dmenu/bash doesn't support that and I know there
  would be some redundant values.  How do you differentiate between band
  Rush and album Rush?
* Adds that path to cmus library.  Should be convenient for all those
  times when I have new music I want to hear but haven't updated yet.
* Second find has a fugly regex escape the brackets.  They didn't work
  in find.
* Live filter gets rid of parens.  They're globs which I don't like, but
  it's the only consistent solution I've found so far.