Partially duplicated and diverged source code for command handling.

Partially duplicated and much diverged source code, partially also source code that is specific to enforcer/signer. This could be improved by adding commands to the cmdhandler in a register-pattern, such that the common code can be held common.
Now duplicate methods are: cmdhandler_create(), cmdhandler_start(), cmdhandler_cleanup() contained in enforcer/src/daemon/cmdhandler.[ch] and signer/src/daemon/cmdhandler.[ch].