Always display/save log header

[Felipe Figueiredo]

MMRRSim::log_header() is currently being called at the end of MMRRSim::init(), which causes it not to be called in case of fatal error from configuration. It should be called as soon as possible.

It is, however, dependent on Mosquito and Trap objects that were not yet created at the point when the logger object is created. This is not a needed dependency, since all variables required are defined in the config object.