checking free diskspace. send warnings (email & logging) and stop recorder if a critical value is reached.

got too many data from pv. data is now filtered => easier debugging. now it is only possible to comment this to disable this function

5 different recorders possible. 'last' missing thing on liquidsoap side: smooth transition between mixer.selects

recording is now part of engine.liq. a redefinition of the recorded source is needed if those two should be separated.

several things: critical socket threading bug from comba resolved. adapted interfaces to pv / tank / database