Goscorer integration and stone removal phase overhaul

[anoek]

This patch updates the stone removal phase in a number of ways:

• Switches our scorer to use https://github.com/lightvector/goscorer which does automatic dame detection and proper seki scoring for Japanese rules
• Adds support for highlighting locations that need sealing before proper scoring can be done
• Alters the toggling of dead stones in the stone removal phase to make it less error prone
• Removes the ability to manually flag locations as dame. Moving forward if there is a problem with dame detection, it's considered a bug.
• Adds a red X to removed stones for clarity