KDDockWidgets 2.0.0

Highlights of the 2.0.0 Release

• Architecture rewrite to support more frontends besides QtWidgets and QtQuick.
  2.0 isn't very interesting for users, but will allow developers to make KDDW
  support other GUI frameworks more easily. Also QtQuick is now better integrated,
  without being shoehorned with ifdefs into the QtWidgets implementation.
  • Split into a view/controller architecture
  • Non-gui logic moved to controllers
  • Each controller has a gui counter part, implemented for each supported frontend
• Uses nlohmann JSON library (MIT) instead of QJsonDocument, for saving/restoring layouts
• Added Config::setStartDragDistance()
• Removed Config::setTabbingAllowedFunc() which was already deprecated in favor of Config::setDropIndicatorAllowedFunc()
• Slint and Flutter WIP. Waiting for these frameworks to support multi-window before finishing.