Replace `connected_nodes` with `connected_edges`

[antonykamp]

Suggested refactoring

Add to the class Nodes the property connected_edges containing the connected edges. This will replace the property connected_nodes. To keep reading access of connected_nodes somehow, calculate the connected nodes based on the connected_edges and use a @property decorator.
Do the same with connected_on_left, connected_on_right and connected_on_head and set_connection_left, set_connection_right and set_connection_head.

Therefore, every writing access of connected_edges and call of set_connection_left, set_connection_right, and set_connection_head has to be refactored.
Affected repositories are

• https://github.com/simulate-digital-rail/orm-importer
• https://github.com/simulate-digital-rail/planpro-importer
• https://github.com/simulate-digital-rail/cli-importer
• https://github.com/simulate-digital-rail/interlocking-exporter
• https://github.com/simulate-digital-rail/track-signal-generator

Advantage of refactoring

With this refactoring, we can identify "Abstellgleise", because we have two different connected edges instead of the same connected node.
Additionally, we can improve calc_anschluss_of_all_nodes. Currently, this function calculates the angles between three edges with their top nodes. This leads to failures if the edge is very long and straight.

Acceptance criterion

• Add connected_edges
• Replace connected_nodes with function and @property decorator
• Add connected_edge_on_left, connected_edge_on_right and connected_edge_on_head property with type Edge
• Use connected_edge_on_left, connected_edge_on_right and connected_edge_on_head in set_connection_left, set_connection_right, set_connection_head.
• Use connected_edges in set_connection_left, set_connection_right and set_connection_head
• Replace connected_on_left, connected_on_right and connected_on_head with function and @property decorator
• Add function to Edge given a top node of the edge, get the opposite one.
• Add function to Edge given a top node of the edge, get the nearest geo node