Improve admin group page performance

Add pagination for projects and members to /admin/groups/:group page

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Add members paginations to admin/project page

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Get group members only if group not nil

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'performance-improvements' into 'master'

Performance improvements

Fixes #1135