Add line2d library
Update realtime editing tests to use Line2D
Update controllers/edit-track to use Line2D
Fix bug where eraser tool doesn't erase on one click
Update frontend linerider stores/editor/display/localstorage to use Line2D
Update test-users to use Line2D model
Fix saving unsaved tracks
Merge pull request #1 from conundrumer/line2d-store

Implement using Line2D for scene storage