Denver's mayor was in town Tuesday to talk about downtown arenas and the need for strong mayors — two subjects close to Sacramento Mayor Kevin Johnson's heart. Building an arena downtown could help reinvigorate Sacramento's core, if the success of Colorado's capital city is an indication, Denver Mayor John Hickenlooper said during the Downtown Sacramento Partnership's annual State of Downtown Breakfast. Last week, would-be Sacramento arena developers outlined seven proposals for a new "sports and entertainment center" in response to Johnson's request for such proposals. All but two were proposed to be built downtown. The same day, a Sacramento Superior Court judge issued a tentative ruli