Show multiple next move markers if a node has multiple child nodes

[herzbube]

Currently the app shows just "A" if the current node has a child node in the current game variation.

New: Show "B, C, D, ..." if the current node has more child nodes.

Unclear:

• Where to start with "A"?
  • Child node in current game variation? Which node should then get "B"?
  • First child node? Is probably the most logical because we could simply iterate from sibling to sibling. However the user will surely want to see which is the one in the current game variation. Use color?
• What to draw if the same intersection is used by multiple child nodes?