XMLUtils: fix
dhcp: fix typos
const fixes (in OMNeT++ 5.0, check_and_cast<> no longer silently discards const modifier)

TODO maybe introduce a check_and_const_cast<> macro as shortcut for
const_cast<T*>(check_and_cast<const T*>(p)) ?
IPv4NetworkConfigurator: added @groups to <interface>
bgp examples: added dummy configurator module to BGPOpen, and updated fingerprint accordingly
bgp examples: irt files replaced with IPv4NetworkConfigurator XML
examples: remove remaining, unused irt files in some examples

ospfv2/fulltest
inet/tcpwindowscale
rtp/unicast
dhcp/wlan: added dummy module as placeholder for configurator
dhcp wlan: pings and routing were not working, fixed
dhcp/wlan: rt files replaced by IPv4NetworkConfigurator XML
mpls examples: added dummy module and updated fingerprint
mpls examples: empty xml files replaced by inline xml
mpls: added empty default for xml config parameters; rename 'conf' parameter to 'config'
mpls examples: use symbolic name instead of IP address
mpls examples: no need for manual routerIds