scanbd Code

Added a callback to scanbd to retrieve the location where the backends are stored
- Reverted split of scanbuttond config dir and lib dir. Use lib dir only
- Major cleanup of Makefile.simple: added Makefile.conf that contains all configuration
This is included from all applicable Makefile.simple
- Rewrote install section of Makefile.simple. Adapted it to latest configuartion and
made it aware of whether scanbuttond is used and only install backends when applicable