[story #005]xuhao&xuxxiaojuan: Add a login.js file, but the ajax return error.
[story #005]xuhao&xuxiaojuan: Fix the POST request, if succeed alert(登陆成功),else alert(登陆失败).
[story#005] xuhao and xuxiaojuan:finish the login,judge the admin and redirect function
[story #005]xuhao&xuxiaojuan: Fix login.js and app.rb.
Merge branch 'master' of github.com:tw-preschool/letusgo-team-c

Conflicts:
	app.rb