v1.3.1

Added support for viewable impression events

• Added: okanjo.ui.getElementPosition will include err if the element position is unavailable
• Added: okanjo.ui.getPercentageInViewport to return what % (0-1) of the element is in the viewport
• Added: Placement constants and handlers for tracking viewable impressions on widgets, products, articles, and adx
• Fixed: Placement configuration url_referrer was ignored if manually configured