Add Polygon shape with variable amount of sides

[Jefwillems]

• Provide an additional or update an example to demonstrate your changes or new features.
• Update the documentation if you introduced new behavior or changed existing behavior.

• I didn't update the documentation yet because i am expecting to make more changes to the bounding boxes/sizes.

• This provides a solution for Add node shape: diamond with label inside #3595

• This issue asked for diamond shapes with the label inside, this is possible now with options: {sides:4, shape:'polygon'}

• Expect review comments and change requests by reviewer.

• Please inspect the behaviour i added to the network basicUsage.html example, i believe i'm doing something off with the sizes/boundingbox

• Delete this checklist from your pull request.
  🙃