invert direction of arrows in hairball diagram

[jhpoelen]

As suggested by @mariestuder in #42 (comment) .

[coding46]

Currently the arrow direction is from "source" to "target".

Just inverting won't answer the question for those bidirectional interactions ('eat' / 'is eaten by'). Maybe a mouseover for links would be an idea?

[mariestuder]

Oh yes....those tricky bidirectional interactions! Perhaps it would make sense to have as a default the the arrows going "up" the food chain and either a different color arrow and/or a mouseover to highlight additional information.