TODO:
 - Dock manager doesn't work as intended when I drag two windows onto it
 - Ensure that dragging items onto the title bar works

Resize sliders
 - Add a button between docked windows
 - Allow the button to be dragged, and it will automatically resize separating widgets

TitleBar dock/undock 
 - Releasing the dragged window over the drop overlay will dock the window
 - Moving the dragged window over a title bar will temporarily dock the title bar and allow you to move it (as in first step)
   - If you release the mouse the window will then be permanently docked at that location

CONSIDER getting rid of mouse event filters for DockManager
 - I can probably convert DockManager into a GUIElement?
   - EditorWidgetContainer as well!
      - Make sure to update GUITabbedTitleBar::tabDragEnd when I do convert it to GUIElement

Polish TOOD:
 - Change cursor icon when window is dragged
 - Prevent docking if available size is less than 20 pixels, otherwise there might be some weirdness

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Other things to remember:
 - Possibly add a way to have hidden widgets in the EditorWidgetContainer (like side-bars that pop on mouse over in Visual Studio)
 - A way to persist window states
 - Also a way to reset all widgets to original locations