it's unused atm

Instead of hardcoding the paths of the node_modules directory we use the node-resolve
plugin of rollup to find the root of the corresponding JS package and calcucate a path from
there.

Resolving a package requires calling an async function, so we have to use await in the rollup config.
Luckily rollup supports configs wrapped in a promise, so we just have to wrap it in a function which returns
a promise.

Since they are no longer in separate repos we no longer need the
gitlab CI config files.

We couldn't do this until now because we referenced them by a relative path with npm.
But now that we reference them by name and yarn handles the linking we can
specify them as normal dependencies.