Improved Python bindings for templated classes

[lelemmen]

Describe the feature you'd like
In native Python, we're never worried about exposing an underlying type to a class. For example, np.array is suited to work with any underlying data type (floats, doubles, complex numbers, ...). I'd like this library's Python bindings to follow the same approach.

Describe what the current code offers in relation to what it lacks
Currently, we have to expose every template class explicitly, using a suffix for the Python class name. This leads to potentially very long names, like LinearExpansion_SpinUnresolved, which isn't very Pythonic nor clean in my opinion.

Additional context
I'm sure it can be done, but I don't know how, yet, so I think it's good to start with a small prototype.