Specify endpoints & edge type for compounds in the default stylesheet

[maxkfranz]

This will make edges behave better by default for compound nodes.

Edges connected to compounds should be beziers and they should use the outside endpoints.

Depends on

• source-endpoint & target-endpoint to specify the intersection/starting/ending points of an edge source-endpoint & target-endpoint to specify the intersection/starting/ending points of an edge  #1613
• Edge shorthand selector #a -> #b Edge shorthand selector #a -> #b #1647