Refactor AST nodes into symtable for library classes/functions

[lam2mo]

@MrBartWolf will post more details here.

[MrBartWolf]

ASTClass.nameClassMap is a static structure holding the signatures for each class. It is used for testing to make sure classes are being created correctly, and checks that new classes don't share a name with library classes. This should really be done with symbol tables so that a static structure doesn't need to be cleared between compilations. ASTClassBlock.nameAttributeMap is pretty much the exact same thing with attributes. Variable names should be checked with symbol tables, not static data structures.

[lam2mo]

Thanks!