fix LAI selection
- added nLandCoverPeriods, nlaiPeriods to namelists
- moved yId, iLai counter into own class aggregateperiod
- moved all land cover and lai related stuff to mo_common_datetime_type.f90
- updated the mo_mhm_mpr_interface.f90 routines
- yet TODO:
- refactor all changed variables
- update restart routines