MPD: Make "search" a substring match.

This seems to be what mpd does I and am rather used to that behaviour. I am
switching on caseSensitive here which may not be what it is intended for but
for now that only get passed through as false from one place so everything
else should still work fine.
MPD: Support "any" as a search type in find and search.

Currently I am just searching all the defined tag types. I am not sure if
there should be a specific order they are searched in or whether we should
just be searching string ones.

Now coerces the tag value to a string.
Merge pull request #233 from toofar/mpd

Make MPD server more like MPD.