add class for common spectrum generation problems
add problem object to the model class
add test for the problems class
add unflag functions to reset the flags
add clear() function to reset the problems
do not throw in the model, only flag problems
add a print function to the problems class
Bugfix: use the particle name when flagging a tachyon
add getter to obtain the problems from the model class
add function which returns true if we have a serious problem