All rights which may have accrued to any person, as well as all rights which have accrued or become vested in any individual, corporation, municipality, or the state, under any of the heretofore existing tax laws of the state which have been amended, modified, changed or repealed, shall not be affected, changed or destroyed, but the same shall remain in force, subject to review and enforcement in the courts of this state, and for the completion of all proceedings heretofore begun for the collection of taxes or the enforcement of all the requirements of such laws.