Replace EmptyList with list of bottom type

[MeAmAnUsername]

Summary
Replace the type EmptyListType() with ListType(BottomType()). Depends on #170.

Todo

• Wait for Allow subtyping lists if elements are subtypes #170 to be implemented
• Add tests?
• Implement
• Update documentation

Reason
It is inelegant to have an edge case for empty lists. This is currently required because lists are not subtypes of each other, but that would be resolved by #170

Implementation
Once subtyping for lists is allowed, replacing EmptyListType() with ListType(BottomType()) should just work. Explicit checks for empty lists to generate warnings should still work after this replacement.

Related issues

• Currently blocked by Allow subtyping lists if elements are subtypes #170