Special symbols in access key

Looks like you can set the access key using special symbols like #, but then this key won't be actually working.

E.g. you can set the key as LeUbCA59#, but when you use it as /login/index.php?accesskey=LeUbCA59# it doesn't work. 

We should make sure we validate the key when saving and fail if it contain symbols that do not supported further in URL.