Admin screen performance degradation for instances with many groups

For instances with a lot of groups (>4-5 thousand) rendering some admin screens might be notably slower (tens of seconds to minutes) due to a lot of JavaScript processing going on.

This was observed for:

• opening repository details on the repository list
• opening the 'edit project'/'new project' page
  There might be other instances to.

This seem to be caused by rendering a lot of items in the DOM (in this case the group names), and expensive processing in skate.js (seems mostly the getClosestIgnoredElement method). Potentially other screens might be affected as well.