Declarative extension list

[GarboMuffin]

Say goodbye to index.ejs and hello to extensions.json

Extension metadata like titles are now stored at the start of the .js:

// Name: Example Extension
// Description: Does a very cool thing. This must have punctuation at the end!
// By: GarboMuffin <https://scratch.mit.edu/users/GarboMuffin/>
// Original: TestMuffin

Because extensions are all defined in a parseable format, we now also generate a JSON version of the homepage, which may be useful for something else

[LilyMakesThings]

You are awesome