Add width and height to SVG image

Beginning from Mathoid 0.2.5 the specification
of a height and width attribute of the image will be required.
This patch gets those information from the SVG and copies
them to the img tag.

See also
Bug: 20202
Bug: 68295
Change-Id: I93e26a9f538acf21aea1501144bb1dd886ae0410