Set workspace in tag/project

[mriehl]

This would allow us to drop override_path entirely. It would also be possible to set the workspace location depending on the tag type (e.G. golang wants projects in $GOPATH/src/github.com/subject/repo) or e.G. projects from "work" in a separate workspace etc.

This would also simplify path computation (always join workspace and project name). I guess if we do this we should also ensure project names are unique across the board (there is already some infrastructure to check project sanity that is performed on load/save).

@bomgar thoughts?

[mriehl]

There is also the question of what happens if multiple tags try to set the workspace. Last one wins (highest value for priority) seems like it would be what is expected in most cases but it could also be a configuration error, I don't know

[mriehl]

I implemented last one wins (higher priority since this is supposedly the most specific)