Implementing intrinsicContentSize

[Ziewvater]

-intrinsicContentSize allows for the PTKView to be used properly in auto layout without having to resort to explicit dimension constraints. Currently, centering PTKView without providing a size can result in strange layouts (ultimately due to the fact that the PTKView does not determine its own size by the sizing of its subviews). An example of such a layout can be seen in the following screen shot: (Here, the thin, centered grey line is the PTKView)

Implementing -intrinsicContentSize fixes this.

[CLAassistant]

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