Closes #85: Add lazyLoad attribute to each mos chart

lazyLoad delays chart drawing until the chart is visible
in the browser viewport.

mos-histogram defaults to false, all others default to true,
matching the behaviour of the charts on the page. Customize by
passing a lazy-load attribute on the chart html element.
Merge pull request #98 from CloudNiner/feature/fix-out-of-viewport-update

Closes #85: Add lazyLoad attribute to each mos chart