Feature #325 Cache ordered messages in ActiveRouter (not for connected)

Do not reshuffle/reorder all messages in every simulation step. Rather cache the lists and reshuffle them in constant intervals. Note: For deliverable messages to connected that is still done, since those might depend on already knowing we're connected.

For the tests an interval of 0.5s was used, which improved performance a little. The default value is 0.0 to keep the simulators original behaviour. There is a setting if it should be changed.