Remove 'fixed' body checks from pe coupling module and replace with reasonable other state
Some functions (mostly the mapping functions) in the pe coupling module make use of the 'fixed' bool to decide what to do. Since this (historic) state has been quasi removed from the pe, those functions should be updated to use one of the following states: global / communicating / infiniteMass / finite. Also the meaning of the 'global' state has been changed and might make some of the provided functionality unnecessary. Thus the pe coupling module has to be checked, use cases have to be discussed, and the changes have to be made accordingly.