Port for 1.13 (17w47a - 18w43a)

Yarn mappings only exist for 18w43b+. We are using them in the yarn branch for versions until 1.14.4. In 1.14.4 mojang released official mappings, so there is no need for them anymore.

We still need support for <18w43a. This issue just refers to versions released after 17w46a, see #1