Montgomery County and Norristown officials turned out Thursday for a groundbreaking ceremony at Theatre Horizon, a new performing arts center in an old Bell Telephone Building on DeKalb Street. The theater company has performed in seven different locations since it was founded seven years ago.  Norristown Councilman William Caldwell says the new theater is another part of revitalization.  Building renovations will cost $395,000 with money coming from a county grant, local revitalization funds, donations from the Wyncote Foundation and PNC Bank and theater fundraising events.  The opening is set for November.