Rework STATS interface
The current STATS interface which can be accessed via "curl -X STATS http://server:8000/" lacks some features:
- Not compliant with HTTP spec:
- method needs to be changed from STATS to GET and with that the target URL has also to be changed
- Sent HTTP-Response headers, define mime-type
Add lines for mount add/remove, for example "ADD /test.ogg" and "REMOVE /test.ogg"
Remove spurious "null null" entries