Allow users to load Style and Domain programs from their vault

[wodeni]

Summary

Currently, the Style and Domain programs are hard-coded into the plugin itself. For this plugin to be at least usable, there should be a mechanism for the user to load their own files. This issues provides two possible designs for this.

Dynamic language ids

A penrose diagram block looks like this now:

```penrose
Vertex a, b, c, d

In this design, the user can set up identifiers for their Style-Domain pairs that will produce objects such as:

```js
{
  simpleGraph: {
    style: "penrose/simple-graph.style",
    domain: "penrose/graph.domain",
  },
  euler: {
    style: "penrose/euler.style",
    domain: "penrose/setTheory.domain"
  }
}

and use the key as the language id in the code block:

```simpleGraph
Vertex a, b, c, d

This will require the plugin to dynamically call the obsidian API to register new language ids (e.g. via `registerMarkdownCodeBlockProcessor`) when the user changes their configuration to add more files from their vault, which I haven't tested yet. 

# Substance front-matter

Instead of relying on the obsidian api, we could also augument the substance language so the user to specify the files to use:

-- type: simpleGraph
Vertex a, b, c, d

...where how `simpleGraph` maps to vault files is also defined by the user configuration, or, even simpler:

-- style: penrose/simple-graph.style
-- domain penrose/graph.domain
Vertex a, b, c, d