python: Make type string identifiers more consistent with the HTTP JSON API

[da-tanabe]

Make type string identifiers more consistent with the HTTP JSON API.

A few under-the-hood changes, none of which should break typical application code but may impact code that uses dazl's DAML reflection capabilities:

• dazl.damlast.daml_lf_1 formerly depended on daml.model.types, as some long-existing types (notably TypeReference) were repurposed for parsing DAML-LF Archives. This dependency has now been flipped in order to make dazl.damlast.daml_lf_1 function more as a standalone package (and to pave the way for code generation of this file instead of manually maintaining its contents).
• dazl.model.types.TypeReference used to be equivalent to dazl.damlast.daml_lf_1.TypeConName and were used interchangeably (because they were the same type). This has changed, and dazl.model.types.TypeReference now wraps dazl.damlast.daml_lf_1.TypeConName.
• The internal structures of PackageRef, ModuleName, and DottedName are now considered private implementation details as a future version of dazl will be changing under-the-hood details.
• Removed some old code that did not work.

This addresses #84.