Selection History - Window enhancements

This release greatly enhances the usability of the Selection History Window.
History entries can now be directly selected (via click) and even dragged out of the history to drop them anywhere in the Unity editor.
Also the selection history now survives an assembly reload after recompiling.

Changed

• Decreased Unity version requirement to 2019.3.5f1

Added

• Enhance selection history window
  • Selectable history entries
  • Dragable history entries
  • Multi selection object counter
  • Auto scroll to current history entry
  • Clear button in context menu
• Recovery from assembly reload
• Clear deleted objects from history

Fixed

• Fix last object being skipped after deselection
• Fix Windows specific functionality not excluded on Mac/Linux
• Fix back/forward mouse buttons being registered when Unity is not focused