Create a common C++ class for ID'd objects

[pshriwise]

Description

We have many objects that use IDs and hold an entry in a vector and map within the openmc namespace. Most commonly, these IDs are read from an attribute on an XML element in the same way. At some point I think it would make sense for these objects to inherit the ID capabilities from a class that handles ID checking/setting and insertion into the relevant vector/map pair.

This would make it more straightforward to add other ID'd types in the future. Source distributions are on my list, for example.

Alternatives

This isn't what I would call critical, so perhaps leave it as-is for now.

Compatibility

I don't believe this would affect compatibility for most users as it's primarily a refactor to reduce code duplication. Though there are perhaps cases code interfacing with the C++ objects directly may be affected (e.g. if an attribute becomes private with accessor methods).