Add ability to group labels of similar purposes : Related labels

Description

I'm setting up global labels to be used on all our projects. We have labels with distinct purposes, for instance, the issue board (e.g: "In progress", "Testing"), the type of the issue (e.g: "bug", "enhancement") and the difficulty level (e.g: "noob", "hacker"). The problem is that all this different labels get mixed up in the global labels admin panel, and it becomes confusing to explain to newcomers how things work here (see image below).

Proposal

Add the ability to create groups of labels and add together labels with similar purposes.

Links / references