Remove a style unused.
Just work!
Extract variables about styles of overlay of jsPlumb connections.
Extract functions about point up and down arrows and labels.
Change function.prototype.call with this to normal function call.
Unify a local variable name of jsPlumb connects to 'connect'.
Remve parameters unused.
Merge pull request #49 from pubannotation/hover_label_with_relation

Hover a label when the mouse is over the associated relations.