Version 2.1.0

Changes compared to 1.x versions:

• internal: migrated framework from Cordova to Capacitor 5, push notifications from OneSignal to Firebase
• tournament: support for team battles, added tournament chat
• analysis: practice mode, threat mode, game replay mode
• correspondence: conditional premoves
• home page: new design with featured game and featured streamers
• blindfold play mode
• new piecesets & board themes
• more translations available in more languages
• many bugfixes and other improvements to stability and performance