By Crispian Balmer RAMALLAH, West Bank (Reuters) - Palestinian President Mahmoud Abbas faced pressure from Western allies on Thursday not to let Prime Minister Salam Fayyad quit at a time when Washington is seeking to resurrect Middle East peace talks. Palestinian sources told Reuters that Fayyad had offered his resignation in a letter to Abbas following weeks of sparring over his handling of the government and an economic crisis afflicting the Israeli-occupied West Bank. ...