Validation of traited input-parameters should return nicer error messages

Comment from Tim:

*If I indicate a wrong value in a parameter field in simulator, for
instance:
-2**-22
gives me
ERROR: Could not launch with no data
from:integrator_parameters_option_HeunStochastic_noise_parameters_option_Additive_nsig
which makes me believe that I have a "data" problem
-1/30000.
gives me
ERROR: Could not launch with no data
from:coupling_parameters_option_Difference_a
a bit clearer, but the top would be something like :"incorrect way of
writing field blabla, mathematical operations are not allowed"