Add admin code management page

- "AdminCodePage" has been added so that users can manage their admin
codes. This page has not been linked anywhere, but may be accessed
through the url: "./AdminCodesPage.jsf"
- The user management page now properly cascades deleted admin codes,
removing any links.
- Added "thickplus" and "thickminus" to the buttons under user
management to make it easier to tell what each will button will do.