Dockerize, bugfix, update

Fix piece-breaking upstream changes

Update and extend documentation

Add shortcuts for new features

Implement move swap/reject

Implement queening, improve mouse handlers

Refactor frontend, extract models and arrows to own files

Refactor file reading and crawl evaluation/troubleshooting

Refactor favorites to database, simplify flask return expressions and cursor finding

Add move unlinking (shallow)

Add righthand details menu, arrow triggers, suggestion listing

Fix checkmate crash

Rework back/forward stacks

Add Practise/Explore modes, fiddle with buggy backstacks when switching modes

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