Egyptian police have detained the deputy leader of the opposition Muslim Brotherhood, about 10 other prominent members and scores of Brotherhood students in dawn raids.   On Thursday, Khairat el-Shatir - one of two deputies to Mohamed Mahdi Akef, the group's general guide - was taken from his home in a northeastern suburb of Cairo. The main target of the crackdown appeared to be leaders and members from the movement who are associated with the students at al-Azhar University. The students had set up a union independent of that vetted by the authorities.