#175 UseCustomCheckboxImages causes text in primary column to use ellipses

[Mike H]

Setting UseCustomCheckboxImages = true and StateImageList causes a miscalculation of the space that should be allocated to the text for rendering. The result is that the text is clipped and ellipses are rendered (despite the overall width of the column).

In Renderers.cs, in BaseRenderer:

• CalculateContentSize calculates required space for the text and checkbox (using the image size).
• DrawCheckBox calculates the checkbox size using CalculateCheckBoxSize (which equals image size), then adds 4 to the return value.
• The returned value from DrawCheckBox is used to reduce the available witdth for text which is less than the calculated width for text in CalculateContentSize