prevent slide CTA from disappearing on scroll

[victor-duarte]

Closes #112

Scroll event added to .Cards is triggered on scroll of the children (.Block) causing calculation to be done against Block offset instead of Cards returning unexpected values.

• Prevent scrolling calculations from being triggered on none .Cards elements
• Update slide CTA initial state to false since the CTA's would only appear after user setup
• Prevent last Block being cutoff when scrolling is available by removing the scroll-padding-left property
• Add aria labels to previous and next cta's

[victor-duarte]

Looks good, well done can you remove the unused class scrollButtonNext?

The class has been removed.