Add world level multi-select movement

[AndyParka]

Summary

• adds a multi-selection box when dragging mouse in the World View
• support Ctrl/Cmd-click for multi selecting levels on the grid
• allows ability to move selected levels together in Free and GridVania world layouts, with Linear layouts retaining selection/highlighting only

Testing

• build locally on MacOS
• open new project as GridVania
• test, save, load and test again
• test feature on existing established project, save, load, test
• all working

Fixes #1160
Fixes #1072
Related to #747