Upstream's implementation has been merged a while ago and is the preferred
way to set fields, as it is the only one compatible with upstream and is
more user-friendly.
This commit deletes the legacy glitch-soc FrontMatter functionality in order
to clean up the code and make it easier to maintain.
Conflicts:
Dockerfile
app/javascript/packs/common.js
config/webpack/loaders/sass.js
config/webpack/shared.js
db/schema.rb
package.json
yarn.lock
A lot of the conflicts come from updating webpack.
Even though upstream deleted app/javascript/packs/common.js, I kept
glitch-soc's version as it unifies JS/CSS packs behavior across flavours.
Ported glitch changes to webpack 4.x
