Group action items by milestone on project detail view

DMT #95978

Right now the milestones here are sorted on milestone name alphabetically.
sort milestones by target date
use new manage.py check instead of validate
Merge pull request #123 from nikolas/milestone-display-on-project-page

Group action items by milestone on project detail view
Merge pull request #129 from nikolas/use-check-instead-of-validate

use new manage.py check instead of validate