COMP: Fixed warning about signed/unsigned comparison

Match the type returned by vtkAbstractContextItem::GetNumberOfItems.

Change-Id: I588632253c62f7624b15b189ca1f3a272bd113a3
Changed to fit the VTK style, separated some logic

Changed to use VTK naming conventions for variables, fixed one or two
stule issues and separated the logic in the CopyToPoints functions in
preparation for adding the scaling logic.

Change-Id: I2057ef5c0b27d19cb024c8a004c4e794fd2faef5
Added scaling to the vtkPlotBar class (and a test)

Added awareness of the scaling factor to the vtkPlotBar class, and a
test to exercise this functionality (with mixed plotting of points, line
and bar).

Change-Id: I55e157012e2618d5d59986ef828f80036188f4c7
STYLE: Minor fixes to documentation strings

Change-Id: I5d9b4ca87539172df2ee58730035bfdf7afdbde3
Merge topic 'charts-double-precision' into master

dd403de2 STYLE: Minor fixes to documentation strings
dc73d916 Added scaling to the vtkPlotBar class (and a test)
043de2d1 Changed to fit the VTK style, separated some logic
da970a2b COMP: Fixed warning about signed/unsigned comparison