cubicweb-jqplot #2465777 csvexport: remove <a> and <br/> from anystring [done]

currently, only <a> removed from series'label

prioritynormal
typebug
done in0.3.0
load0.100
load left0.000
closed by#202d96d656b9 csvexport: cleanup every string values, not only labels, and also remove <br/>. Closes #2465777