Fixes #1661.

Checklist

• I have included examples or tests (there are enough examples demonstration clipping I think)
• I have updated the change log
• I am listed in the CONTRIBUTORS file
• I have cleaned up the commit history (use rebase and squash)

Changes proposed in this pull request:

• Move responsibility for clipping out of the Render methods of Series and Annotations
• Remove DrawClippedXxx() extensions
• Avoid unnecessary clipping calls

Remarks

• The PathAnnotation.ClipText property for obvious reasons was broken by these changes. As it didn't quite seem to fit the overall design anyway and appears not to be very widely used, I decided to remove it. The only place that actually used this property was the Train Schedule example. As I quite liked this example I fixed it using an Axis for the station labels, which seems more sensible to me anyway.
• The CandleStickAndVolumeSeries could only be fixed by a rather ugly hack. If anything, this indicates to me that this series violates some of the design principles the library is built around, so I applied the hack and marked it as obsolete with the recommendation to use separate CandleStickSeries and VolumeSeries instead.
• I noticed that Annotations could return different clipping rectangles depending on whether you use Annotation.GetClippingRect() or the ITransposablePlotElement.GetClippingRect() extension. As this is not an ideal situation, I slightly changed the design here to make it more consistent.

@oxyplot/admins