[3977] Name change requests are now generated when lease is reused.

[3977] Name change requests are now generated when lease is reused.

This change triggered a lot of code refactoring for generating the
NameChangeRequests. Long story short is that the functions responsible
for generating NCRs from the lease information have been moved to
the libdhcpsrv where they better fit and where they may be used
by both allocation engine and the servers.