svg-edit: Clean up JSLink object

The JSLink object should be a mere bridge between the JavaScript
functionality within the QWebKit viewer and the Python code.
JSLInk should not access anything from the document or app or mainwindow
ect. It should only accept signals from JavaScript and defer them to the
View object.
svg-edit: defer saveSVG to View object
svgedit: rename setCursor signal to onClick
svg-view: highlight "forever" on hover

There is no need to unhighlight after 5 seconds. I think that as long as the
mouse is over an item it should be highlighted.
svg-edit: some cleaning up of signal/slot code
svg-edit: remove obsolete setSaved function