Tweaks to MGC to deal with cases

The run card in MG is not case-sensitive, and if a variable is set multiple times it takes the last setting. That means up to now if iseed and iSeed were set, the one set second was used. That saved some users who used different capitalization from what's found in the run card, but is confusing. Now we rely on setting everything to lower case and doing a case-insensitive match, and then using the capitalization specified by MG5 if a setting exists. This should help clarity for users.

Thanks to @tpelzer for the report!