Partial Chrome fix and persistent drawings

This fix adds an empty div as a sibling of the SVG so that tinymce
on Firefox does not delete the svg tag.

This fix also makes the program not rely on the innerHTML tag so
that one can insert images in Chrome.  (There are still more fixes
to make this work under Chrome including selection and editing
already existing SVGs, which is now broken with this commit.)

Also, the SVGs now have the correct size in the embedded view -
previously their size was unspecified and relied on the default
size for an SVG, which chopped off some of the image.