Simplify dependency setup

[slavaschmidt]

For now we have different repositories for different dependencies from Zalando's ecosystem.

We probably should consider putting all of them into one single repo.

We also definitely should stick to uniform repository layout (compare IvyStyle for sat-plugins to maven style for beard)

[slavaschmidt]

It seems that we cannot do the simplification in easy way. SBT expects the repository to have an ivy layout for plugins. Other dependencies like beard and son-reference-... published in maven style. Therefore we need two different repos with different layouts.