'Fix' for Chrome type error

Chrome throws a type error on `new Image()` but not with
`document.createElement('img')`, when calling drawImage
Fix for elementUnderMouse/hoverInfo on Dash

Relative positioning of each dashboard module renders offsetParent
ineffective for our purpose. JQuery offset always uses the document as
the base, which is what we need.
Merge pull request #334 from gavin19/master

Fix for Chrome type error