draw markup: clear precedence in which markup types are drawn (#349)
draw markup: clear precedence in which markup types are drawn (#349)

change details
- move numbers can now be drawn mixed with other markup; previously
  when move numbers were drawn no other markup could be drawn at the
  same time
- move numbers still have the highest priority: no other markup can be
  drawn on a specific intersection where a move number is already drawn
- symbols, labels, the last move symbol and the next move label can no
  longer be drawn on the same intersection; previously it was possible
  that these were drawing over each other
- the exact order of precedence is: move numbers, symbols, labels, last
  move symbol, next move label
- refactoring and moving around of code in SymbolsLayerDelegate to
  improve the code structure

herzbube/littlego,herzbube/littlego,herzbube/littlego,herzbube/littlego,herzbube/littlego