As an administrator user I can control who can create versions so the version namespace doesn't get poluted with invalid versions when people mistype in Fix Version

Acceptance Criteria

• Users with the Create Versions permission will be able to create versions in the way that it is done currently, typing into Fix Version or editing releases on the Releases screen.
• Users without the Create Versions permission will be able to browse existing releases on the Releases screen and in Fix Version will be able to select an existing version but not create a new one.