Dazl

Fix broken enum support.

Expose a management endpoint for configuring bots at runtime.

* Experimental support for adding/removing/pausing/resuming event handlers dynamically.
* Compatibility with DAML SDK 0.13.16.

* Made dazl responsive to the `DAML_LEDGER_URL` environment variable so that if a URL is not specified in code, it is read from the environment instead.
* Factored out some typical dazl boilerplate into a new API, `dazl.run`.
* Changes to how dazl is configured. This breaks backwards compatibility in the `dazl.client.config` module, so if you are referring to any of those classes directly, there may be minor code changes required (this is not common).

Drop deprecated symbols.
Formally drop support for all DAML SDKs before v0.13.x.

* Add support for more DAML-LF types.
* (Experimental) add support for generating a scenario from a series of Ledger API commands.