uac_registrant: add some sanity checks during module init
(cherry picked from commit 2998f06e766e8ce8a1427539ecdddf9c851949c5)
uac_registrant: add some sanity checks during db record(s) loading
(cherry picked from commit 0181bec67c925c2682e92b1d4dafdbf4d2b38a09)
uac_registrant: print an error if registrar imposed expires to small
(cherry picked from commit c616b080da6bac0101b69361fec60bf14cd6ae8a)
uac_registrant: documentation updates
(cherry picked from commit cca642b54c8fb6f5324bad65e24b39b1ae2ee010)