BUGFIX: Previously, newly added Needs received a visibility ID of NULL in the DB, despite having the "Public?" checkbox
checked. This caused two problems: (1) should the flexible need be made private, the sign up form would throw this
error: Project has no volunteer needs defined; and (2) user-added Needs would not appear in the dropdown unless the
user first unchecked then re-checked the "Public?" box.
Refactor dropdown in vol sign up form to use a more pure JS-based approach, as setting display:none on option elements doesn't work in all browsers.
Merge pull request #114 from fjg-conflux/signup_bugfixes

Signup bugfixes