Developer role can create/edit/delete milestones

Description

Developers should be able to create Milestones themselves since this is a fairly routine task. Master level also gives other permissions which developers should not need.

Requirements

• Developer role can create/edit/delete milestones
• This applies to project milestones. I.e. developer role for that project has permission.
• This applies to group milestone. I.e. developer role for the group has permission.