added signature column

added "signature" to the list of columns returned by the contact class
Added isAdmin condition for sensitive acct fields

Added isAdmin condition for editing sensitive fields in a user's
account.
Changed/removed improper account editing check

Removed restriction for non-admin users to edit their own account
details.
Added signature column to Users class/table
Added signature field into user's details

Added signature field into user's details page for when adding new users
and editing of info.