cubicweb-jqplot #2277781 ability to print a graph [validation pending]

this is currenly broken at best (eg right click then 'save image' get a black png, and this won't include legend, axes & all)

prioritynormal
typeenhancement
done in0.2.0
load0.500
load left0.000
closed by#e4721f06e8f2 add ability to print graph by generating a canvas in a new window with everything inside. Closes #2277781