WIP: Rewrite 1p Basis

[cortner]

This will provide a slightly less generic implementation of the 1p basis, but in return we will significantly reduce the amount of pointless wrapper code which should make ACE.jl more maintainable. In addition we will gain flexibility in other ways since this will be a step towards a "more differentiable" ACE.jl that will allow us to differentiate w.r.t. any parameter anywhere in the model.

• This is a big step towards Rewrite ACE.jl as a Graph #116
• it will also get us closer to Species-dependent radial basis #113

[cortner]

What's left to do:

• incorporate the distance transform into the value extraction
• improved rrules
• put the basis components into a named tuple instead of tuple to prepare for the nested parameters
• revive the linear transformation of the basis

maybe all of these could be separate PRs.

[cortner]

I'm going to keep things separate, merge this and start another PR.