`to_contracted`: when the morpher is called with simplify it always drops selfloops and does not exploit the options of to_simple

[gi0na]

The morpher to_contracted calls to_simple without allowing to pass options.
In many cases, though, we may want to keep selfloops when e.g., collapsing nodes to their group "meta-node", so that edges within groups are not lost. I propose to make the arguments of to_simple visible from to_contracted.