Slower scrolling, prevent navjump, prevent scrolljump, fonts for Polish

Bug 822344 - slow down scrolling when covering longer distances
Bug 831332 - switch to Georgia for Polish (Vollkorn lacks characters)
Bug 822341 - pad body to minimize visible jump when modal overlay disables scrollbars
Optimized promo video thumbnail
Added classes for Czech and Russian font switch
Using Math.abs for scrollTime

Also added an else to set scrollTime back to 1000 for short scrolls. Probably a cleaner way.
Added body class for Slovenian