Acknowledging that Los Angeles is the epicenter of a global gang crisis, fueling violence from Guatemala to Russia, law enforcement officials from around the world will meet this week to tackle the scourge. LAPD Chief William Bratton will open a three-day summit today to discuss the migration of gang members from Southern California to their homelands, bringing a culture of violence and terror. "We are seeing the international gang problem growing by leaps and bounds," said Lt. Gary Nanson, head of the Los Angeles Police Department's Valley gang unit. "They have opened up the door for the local criminal. They...