Basically complete add users function.
Modify user groups mechanism.
Refactory CSS file.
Re-encapsulate the PHPExcel library.
Modify README.md.

Signed-off-by: Xie Haozhe <zjhzxhz@gmail.com>
Merge branch 'master' of https://github.com/zjhzxhz/stumgr

Conflicts:
	application/libraries/lib_accounts.php

	modified:   application/libraries/lib_accounts.php