Feature: Draggable window improvements

[ATMarcks]

• Modularized the draggable windows
  • Created a DraggableWindow window component, removing reuse of the window background/x button/drag handle styling code in the TexturePicker and the Explainer
  • Stylized draggable windows can now be simply created like the following:

    <DraggableWindow hidden={hidden} setHidden={setHidden}>
      <div>I can be dragged around</div>
    </DraggableWindow>```
    

• Added a WindowManagementProvider which tracks the state of the most recently clicked/opened window and ensures it is on top of the other windows (has a higher z-index)
  • The draggables now act more like Windows or MacOS; if you have both the explainer and the texture picker open, and they are overlapping, clicking on the window that is behind the other one brings it to the front
• Fixed issue with title bar rendering
  • The pattern no longer clips behind the "X" button
  • 
  • I think this was the original intention given the flexbox styling on the parent

Let me know if this is too much for one PR, I can cherry pick the commits out into two or three branches

[davidar]

Nice, thanks for cleaning this up