Add ability to filter on track metadata in hierarchical track selector

[cmdcolin]

This is a random idea that popped into my head but if the hierarchical track search could return results for metadata matches on tracks it might be interesting xref #1707

[rbuels]

First level of this would probably be the text filter box also operating on all the track metadata.

Second level, I could see maybe supporting a text query language similar to the one that github uses for the issues list, coupled with (later) some UI to construct the queries graphically.