§ 421. Powers of attorney to be filed and registered. Before any person can convey, charge, incumber or otherwise deal with any registered property, or any estate, right or interest therein, as attorney in fact for another, the deed or instrument empowering him so to act shall be filed with the registrar and a memorial thereof shall be entered upon the certificate in the title book, in like manner as in the case of a charge or incumbrance. A revocation of such power of attorney may be registered in like manner as such power of attorney was registered.