Removes the promote icon button and adds an action menu.

The action menu has different content depending on permissions,
milestone attributes and what page the user is on.

On the project milestones page, the action menu can show Close, Edit,
Promote and Delete actions for users who can perform those actions.

On the group milestones page, the action menu can show Close, Edit and
Delete actions.

On the user's milestones dashboard, the dropdown can only show Close and
Edit.

Changelog: changed