By Nidal al-Mughrabi GAZA (Reuters) – Mourners flooded the streets of Gaza on Friday as they carried the shrouded bodies of 21 people, including at least eight children, killed in a fire in an apartment block where residents had planned to celebrate the homecoming of a relative. Most of the dead were members of the Abu Rayya family, their bodies wrapped in Palestinian flags and brought into a mosque for prayers over their souls, before being buried at the Cemetery of Martyrs east of the Jabalia refugee camp. The Islamist Hamas group, which has ruled the Gaza Strip since 2007, gave the victims …