Adapt to changes in pandapower v3

[danielfeismann]

With pandapower version 3 there are some changes with respect to handle geocoordinates. See pandapower documentation on this.

This also caused tests to fail when updating the dependency in #11

Todo:

• adapt methods to changes
• if necessary, adapt tests to changes
• update pandapower dependency

[danielfeismann]

Same needs to be done at pp2psdm, see here