The Upper Gwynedd Commissioners have approved a budget for next year that does not include a property tax increase.   Township officials kept a lid on expenses by deferring some capital projects but there won't be any layoffs or cuts in municipal services.   Property taxes have remained stable in Upper Gwynedd since 2001 when the millage rate was actually cut by 33%.   The budget also includes a homestead exemption that allows qualified homeowners to shield $30,000 of the assessed value of their property from taxation.