Cleanup & expose types in mw.Api

- expose all types within `mw.Api`
- split interface paths into sub-namespaces, allowing to use type aliases to reduce type names when desired
- add deprecated type aliases, mapping old naming scheme to exposed (and renamed) types
- fix handling of `required` values: if a site says a parameter is required and another one says it is optional, then we want to make it optional
- cleaning up some stuff, started to document some things
- move types to a separate declaration file to use the (easier to read) TS syntax