Move some functions out of url_helpers.c into utils.c

Move

    username_to_name() and
    send_template()

into utils.c

This is the first step in removing url_helpers.[ch]

Signed-off-by: Andrew Clayton <andrew@opentechlabs.co.uk>
Move match_uri() from url_helpers.c into url_handlers.c

We can also mark this function as static as it is only used in
url_handlers.c

Signed-off-by: Andrew Clayton <andrew@opentechlabs.co.uk>
Move some functions out of url_helpers.c into audit.c

Move

    check_auth()
    is_logged_in()
    display_last_login()
    create_session()
    set_user_session()

into audit.c

We can also now mark get_last_login() as static as it is only used in
audit.c

Signed-off-by: Andrew Clayton <andrew@opentechlabs.co.uk>
Move remaining functions from url_helpers.c into csrf.c

Move the CSRF mitigation functions into a new csrf.c file.

Signed-off-by: Andrew Clayton <andrew@opentechlabs.co.uk>
No longer include url_helpers.h

Remove the url_helpers.h include from db.c and url_handlers.c as it no
longer contains anything.

Signed-off-by: Andrew Clayton <andrew@opentechlabs.co.uk>
Remove the remnants of url_helpers

Signed-off-by: Andrew Clayton <andrew@opentechlabs.co.uk>