BUGFIX: fix neos-ui-extensibility by transpiling it to JS

[dimaip]

We should transpile all packages that we publish to npm.
For now I started with positional-array-sorter and neos-ui-extensibility.

Don't mind the beta version, will be overwritten by next release.

Problems to solve in the future:

1. it's not possible to build both subpackages and the UI itself in watch mode. For now it's not a big issue as we don't have many subpackages with separate build steps, but that would become an issue if we'd want to publish it. HELP WANTED TO IMPROVE IT.
2. Subpackages have to be built in the order they depend on each other. So far it just concides with the alphabetical order, therefore it works.

Perhaps smth like this could solve these problems in the future: microsoft/TypeScript#17611