last bits and pieces for https://github.com/opnsense/core/issues/117 although rc.filter_synchronize really needs a rewrite at a later moment.

Has it really been this way forever?  While there, chain
mwexec_bg() throgh mwexec() to avoid duplicated code and
increase error reporting.

daemon(8) will completely detach and keep running so maybe that
will be one step closer to reliable firmware upgrades.

replace xmlrpc server and include example stub, legacy methods not implemented yet. client also needs some work