Create Issue-only projects

Similarly to gitlab-org/gitlab-ee#3839 I would like to have the ability to use projects for Issues only. At our org we have hundreds of projects in GitLab, across multiple Groups. In order to get a nice overview we thus have a project that contains only issues mostly written for management and not the technicians.

To make this project "look and feel" better I would like:

• Start page to be Issues (List or Board) and not Files/Readme
• Reduce the number of links on the right