center image caption as it used to be
move carousel background fill color and opacity to css

Also when the width of each item was rounded to whole pixels the right margin disappeared. Better to leave the width w/ fractional pixels.
Merge branch 'upstream/master'
can now append to Image and CaptionedImage

these changes duplicated a lot of existing code. Illustrating the real need to figure out how to implement base classes and other inheritance.
Merge branch 'origin/master'
Merge pull request #20 from mlippert/widget-refactor

Latest image/carousel changes