mlv_snd and dual_iso support for mlv_lite
Created originally on Bitbucket by g3gg0 (Georg Hofstetter)
This pull request contains changesets that:
- add mlv_rec_interface.h for a module<->mlv_rec callback registration which allows multiple modules to receive its callbacks
- add DISO block to dual_iso using that interface
- change mlv_snd to use that new interface
- change mlv_lite to supply that new CBR interface
- change mlv_lite to provide blocks that other modules can fill and queue for writing
along with that, other things got also added which are also part of unified
- change audio backend to use ml-cbr for "asking" if recording is enabled