Added helper methods to UserDatabaseManager

- getUserListOfType:
- createChildWithName:password:andProfileImage:
- createGuardianWithName:password:profileImage:andEmail:
- isAuthenticUser:forPassword:
- save

Updated the following the Following objects to make use of these methods

- LoginPromptViewController
- LoginViewController
- AccountManagementViewController
Added -profileImage and -setProfileImage: methods in User