Allow embedding of HTML templates

[mrmiguu]

Give developers the option to embed raw string literal HTML templates in their components as an alternative to having the markup separate in another file (e.g. App.html).

This will improve developer context switching (see Ui as Code section), or at least give developers the option if they want to write their Ui this React/Vue-way.

This will also utilize VSCode's Go extension down the road for when it allows highlighting of HTML inside raw string literals.

(I tried this and this, but so far neither utilize VSCode's HTML language server. The first one highlights correctly (which is the most ideal) but renders everything else as plaintext. The second one is a butchered highlighting of the current Go syntax, but at least recognizes template tags.)