Cookie name

Changed cookie name to work as subset of whatever Cookie is called. The cookie is called `CakeCookie` by default. And the way this plugin was using it, the cookie was getting written as `CakeCookie[CakeCookie]`. Now whatever the cookie is named gets an appended value of `remember_me` by default.

This is configurable via the settings. So, in the AppController, I now set `$this->RememberMe->Cookie->name` equal to my Application's name so the Cookie gets written as `APPNAME[remember_me]`.