Added member edit/create page to admin area (closes #46)

#### Changes: ####
- Add button to manually create new member from member list
- Add page to view/edit the details of a member
- Add tests for new edit/create functionality
- Update member signup page so users can't update their details with the same email address (this was done to simplify the business logic, sorry for lumping it in this commit)
- Update tests for signup page update