Sabaki v0.50.0

Added

• Complete overhaul of the engine handling system, more than two engines can be
  attached and given player/analyzer roles, also not blocking the user from
  editing while generating moves
• Support for KataGo's non-square boards
• Ability to hide the winrate graph (#608)
• Display winrate and winrate change above the winrate graph (#620)
• Add macOS specific standard keyboard shortcut to close window with
  Command+W (#625)
• Add keyboard shortcuts for scoring/estimation (#345)

Changed

• Board transformations (rotation/flip/inversion) are now temporary and faster,
  transforms coordinates as well, located in the 'View' main menu, and have
  dedicated keyboard shortcuts
• Removing root node will now delete all other nodes and clear the board

Fixed

• Fix 'Update Result' not working in the score drawer (#580)
• Fix comment not updating when exiting edit mode too fast (#584)
• Fix comment text getting erased while in engine analysis mode (#637)