Check unit consistency in input files (works only with GeV and MeV right now)

Up to now, any string suffix in the input file after a number was completely ignored.
Therefore, the two strings "set Foo:Bar 91*GeV" and "set Foo:Bar 91*MeV" were treated
exactly the same. The unit is purely determined by the chosen base in the cc file.

This patch introduces a warning for mismatched values only for MeV and GeV, and enforces
bare numerical values without any suffixes otherwise. Also, only Parameter type is checked
ParVectors are unchanged right now.

A proper handling of this requires a more fully featured parser of dimensioned values
which the Interface classes should use instead of istringstream parsing.