Base & Responsive Embeds Update

Base Embed
• Moved default vertical padding from section to container
• Renamed --page-padding variables to --padding-horizontal
• Renamed --section-vertical variables to --padding-vertical
• Renamed [section-top] & [section-bottom] attributes to [padding-top] & [padding-bottom]

Responsive Embed
• Changed --page-padding--main to --padding-horizontal--main