Functional Cookies

Implementation of cookies. Each user gets the same id each time. Cookie
is set to expire after one year (but that can easily be changed).

Multiple tabs do not generate multiple sliders. If the user has
multiple tabs with controllers, they all have the same id and link to
the same slider. If the user deletes a tab, their slider disappears
(even if they have other tabs/controllers open). However, I don't think
this is a huge issue because I doubt many people will try to use
multiple tabs and the problem is resolved by simply reloading the page.