TLU producer's requirements now found (and installed) through CMake & minor cleanup

The binary files required by the TLU producer (firmware & ZestSC1 driver package) are now searched for by CMake; if the files are not found, they will be copied from the AFS share to the local ./external folder if AFS is available.
The discovered path to the firmware files is hard-coded as default to the TLU producer at compile-time.

other minor changes:
- update of READMEs
- fixed warning in TLU producer
- removed stale symlink