Plugins: use .setAttribute('display', null) instead of display: inline or display: block

[titaniumbones]

We hide plugin instances with display: none, but prevent users from styling instances directly when we use .style.display = 'block|inline'. Would be better to reset to null, which resets that parto f the tag's style attribute, but unlike unset or reset, doesn't override stylesheet declaration.

[titaniumbones]

I've actualy been going through and using unset as the new value, which is perhaps cleaner.