[e4-dev] CSS now supports gradients

[Kevin McGuire <Kevin_McGuire@xxxxxxxxxx>]

The CSS support now supports gradients
(yeah!).
For CTabFolder, it uses the CTabFolder
specific gradient support.
For other widgets, it draws the gradient.

A few notes:

1) The original TK-UI project favors
the syntax:
        background-color: gradient,
                rgb(140,140,140),
                rgb(48,48,48),
                100%;

But the CSS support is quite happy to
not need the word "gradient" and to not need the commas. The
syntax above does work too though. TBD.

2) It's legal to not specify any percents
for the gradient ranges, in which case default ranges are calculated based
on equidistance between the colors.