Add named enum class compatible with parameters

[timsnyder]

Did we ever make it so sparta::Parameter can be of types std::is_base_of<sparta::util::Enum,T>?

By this, I also mean that in the sparta::Parameter specialization for sparta::util::Enum, the parameter validation would come for free (i.e. only strings that map to enum values would be acceptable parameter values and the helpstring would automatically enumerate the allowed values when printed out in a verbose final config or wherever).

[klingaard]

I don't think so, but it's been a while since I took a look at adding enum support (in general) to a parameter. That'd be really neat feature to add esp if we use sparta::util::Enum