The provisions of this chapter relating to the registration or licensing of any person, firm, or corporation, including the requirement of a bond with the state of Washington named as obligee therein and the collection of a fee therefor, shall be exclusive and no political subdivision of the state of Washington shall require or issue any registrations, licenses, or bonds nor charge any fee for the same or a similar purpose: PROVIDED, That nothing herein shall limit or abridge the authority of any city or town to levy and collect a general and nondiscriminatory license fee levied upon all businesses, or to levy a tax based upon gross business conducted by any firm within said city: PROVIDED, FURTHER, That nothing herein shall limit the authority of any city or town with respect to contractors not required to be registered under this chapter.