ALEPPO, Syria — Their names were Issa, Ahmed and Sheik Mahmoud Qasim. They were fathers and brothers. They were students, teachers and laborers. And, last week, they were all killed by tank fire. They are not alone. The Syrian conflict has now dragged on for 18 months and cost the lives of tens of thousands of people. The dead represent all kinds — civilians, rebel fighters, regime soldiers and of