Patch html2canvas to jump back to previous scroll position after parsing (+1 squashed commit)
Squashed commits:
[6b690f5] Previous html2canvas scroll fix was jumping back too early
Split link tag onto separate lines
Attempt to fix issues with Chrome

Instead of the button triggering the image being created and downloaded,
the image is created by the Draw Page button, with the link updated at
that point. The link points to the data: URL, and with the download
attribute provides an acceptable name for the provided file.

A button is embedded inside the link for appearance.
Fix IndexSizeError DOM Exception when there is no output