Native Group Milestone page needs same info as Project Milestones

Description

Currently the native group milestone page just has View Issues or Merge Requests in this milestone message with no issue lists, which the project milestone page does have. There is a milestone cleanup issue https://gitlab.com/gitlab-org/gitlab-ce/issues/35833 but this doesn't look to address this request.

Proposal

Have the Group Milestone page show the same information as the project milestone pages.

Project	Group
Screen_Shot_2017-09-12_at_9.51.10_am	Screen_Shot_2017-09-12_at_9.50.53_am

Links / references

• Group Milestone
• Project Milestone

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.

• Feature assurance
• Documentation
• Added to features.yml