move daemon code out of dhcpsrv library

daemon.{h,cc} defines a few common things: get version, pid file, config file, ...

It should clearly be moved from the dhcpsrv library to somewhere else. A few proposals:

• move it the process library (make sense but add a dependency to old server code)

• move it to config (or similar) library

• move it to its own library

IMHO the last option is the best one but some can have a concern with an increasing number of libraries.