change StudentInfoActivity.java's CRLF to LF
move some Strings in StudentInfoActivity to strings.xml

修改 把一些StudentInfoActivity中的字符串常量（“姓名”、“学好”等）移至strings.xml
move codes who read file to doInBackground method

修改 把读取文件的代码移至doInBackground方法内
avoid NullPointerException after FileNotFoundException
fixes FC error when update scores

修复 更新成绩时，没有及时关闭cursor因而使用过多资源导致的FC错误
修改 默认开学日期