Maybe move some functions / functionality from mtca.py to board.py

I think _create_dbs() should be moved to Board class since it operates on boards.

Most of the functionality from fill_dbs() should also be moved to Board and Sensor: fill_dbs() in MtcaChassis should look something like this:

for b in self.boards:
    b.fill_dbs()

while fill_dbs() in Board should look something like this:

db = self._create_dbs()
for s in self.sensors:
    s.fill_dbs(db_file_name=db)
self.replace_macros(db_file_name=db)