1637 dynamic keywords

[rprospero]

The primary change here is that every keyword is now contained within a specific KeywordStore. There is no longer a static singleton vector in either KeywordBase or in KeywordStore. This leads to a couple of other changes.

1. Since there is no static singleton, removing references to an object in CoreData involves removing the references in every module of every layer. This is handled in the objectNoLongerValid function in coreData.cpp. This is now a function in the module and not a private function in the class because it needs access to the Module and ModuleLayer classes in order to be built. This wouldn't be an issue, but it's a template function, so leaving it in the .h file creates an import loop.
2. The Module and ModuleLayer classes now need mutable access to CoreData, since they might be removing references from it (an obviously mutable action). This has resulted in the change from OptionalReferenceWrapper<const CoreData> to Core Data*. I did use a const_cast in layerFuncs.cpp rather than update the entire call chain to provide a mutable CoreData reference, but I'm willing to change this if other people find it upsetting.

This closes #1637

[trisyoungs]

I confess I'm a little confused why the const_cast and the conversion to a pointer is necessary since, as far as I can see, the CoreData reference was passed non-const down the chain anyway. Indeed I just tried to revert that change locally (i.e. go back to OptionalReferenceWrapper<CoreData>) for both models and all seems to work as expected...

[trisyoungs]

Pedantic as I am I would move this up a few lines so as to make the "list" alphabetical.

[rprospero]

Not only did I move Isotopologue up a few lines, I also moved Module down a few lines. That leaves gets the whole thing alphabetised.

[rhinoella]

👍
Also agree with what @trisyoungs mentioned regarding the const_cast