Added chemistry to the possible reinit cases.

In addition to meteorology and aerosols, chemistry can now be automatically be continued with the reinitialization system. Further, the switches to turn on and off the reinitialization are changed as follows:
Instead of REINIT_FULL_[MET|AERO], there is now CONTINUE_[MET|AERO|CHEM]. Turn it on (set to True), if you want to continue with the meteorology, aerosols and/or chemistry. Turn it off (leave out or turn off False) if you want to reinitialize this data or do not use it.