Migrate website generation from Stencil templates to Plot DSL

[tothambrus11]

The current approach for website generation is to use an html templating library Stencil. This proved to be very error-prone to work with, and it's also unbearably slow for large number of templates. When using it, we use all Swift's type safety, guarantees and compile-time optimizations, making the experience similar to a dynamic language.

We should experiment with switching the website generation to be done fully in Swift, and see what it would unlock performance wise.