Move authority-mode options into dirauth module
These are "v3authoritativedirectory" and "bridgeauthoritativedir".
Also we should be away that lots of the code indirectly asks "are we an authority": that should probably be something that we reconsider or redesign. We don't want most modules invoking the authority module.
This might also mean that authmode.c belongs in src/core? There could be a better solution here.