Add simple ObserverFrame visualization

[FilipAlg]

This PR adds a ObserverFrameRenderer component for visualizing single ObserverFrames and an ObserverFrameRendererManager for rendering all ObserverFrames in the scene using the same set of settings.

Both these classes contain the same options for visualizing ObserverFrames:

• Size of the drawn lines
• Alpha of the drawn lines
• Right handed visualization of the frames
• LineDivisions when drawing the lines
• DrawMode of the lines, with options being to draw lines using GL.Lines or Unity Gizmos

[FilipAlg]

Not quite sure how the ObserverFrameRendererManager should behave in edit mode yet. Keeping this as a draft for now.