Add group and project count badges to group and project navigation items

The following discussion from gitlab-ce!18425 should be addressed:

• @godfat started a discussion: (+13 comments)

  This can be wrong: ...

In gitlab-ce!18425, we've added badge count for projects. The plan was to also add a badge count for groups (see screenshot below) but this requires a concrete plan for further changes in the BE. See the discussion above for more details.

Screenshots

Explore	Your Work	User Profile

Proposal

• The badge should follow the same styling pattern as used for Issues, for instance. Ensure to abbreviate large numbers.
• Define what the displayed number should include: Only active groups and projects? All? Including or excluding archived content and content pending deletion?