detection of upside down text path and handled by flipping source and target
center edge text along path between source and target (results in more pleasing looking graph, and way less complexity than trying to render close to source and flipping that in case of upside down)
edge text becomes darker and slightly larger on highlight, to make it stand out more
some opacity on non highlighted edge text
remove edge animation that is no longer working since conversion to path, this will be handled by #55
Fixes #54