Provide guidelines for the Metrics Team's Java projects

This is the parent issue for defining

• contributor's guidelines
• coding style guidelines
• release process description
• (more?)

for java projects.

This issue serves for discussing "meta" questions like finding a central location and defining the structure.

The central place could be another git repository metrics-team-meta (or some better title), which could hold all documents like coding style guides for the various languages used by the Metrics-Team, guides and documents covering more than one Metrics-Team project, and other docs like the road-map.)