vtkChartXY did not use the space used by the title text and top-axes to
determine where to place the title text. That resulted in cases where
the title overlapped the top-axes labels or for larger font sizes,
simply didn't have enough room. Fixed that by ensuring that the title
placement/border determination code uses the title text's size.

Updated TestLinePlotAxisFonts test to test this new functionality.

Change-Id: Idac42b970eb27ebbaee95adf43748d79747cd1dc