[dw-free] screenshots for layouts

[afuna]

[commit: http://hg.dwscoalition.org/dw-free/rev/efcab63518c5]

http://bugs.dwscoalition.org/show_bug.cgi?id=680

Add screenshots for Boxes and Borders Gray, Stepping Stones Purple, Basic
Boxes Green. Also change the default layout-type to match the screenshot
(all layout-types/columns are available in each of these layouts)

Patch by piranha.

Files modified:

• bin/upgrading/s2layers/basicboxes/layout.s2
• bin/upgrading/s2layers/boxesandborders/layout.s2
• bin/upgrading/s2layers/modish/layout.s2
• bin/upgrading/s2layers/steppingstones/layout.s2
• htdocs/img/customize/previews/basicboxes/green.png
• htdocs/img/customize/previews/boxesandborders/gray.png
• htdocs/img/customize/previews/steppingstones/purple.png

( Diff: 7 files changed. )