Allow editing versions in admin/projects/{project}/releases

[rwinch]

When performing a new release, it takes multiple steps because the version cannot be edited. For example, if 5.4.2 is the current release of Spring Security, then 5.4.2 and 5.4.3-SNAPSHOT must be deleted, next we must add 5.4.3, and then 5.4.4-SNAPSHOT must be added. It would be much easier if we could edit the version