redesign CELEMENTS.image.SlideShow and implement InlineSlideContainer,
start OverlaySlideContainer
refactor image.SlideShow class to ContainerOverlay, ContainerInline,
image.SlideShow and ConfigReader
remove countSlideNum and currentSlideNum css display:none rule (it can
now be configured in rte celimage picker)
add default layout for currentSlideNum and countSlideNum
add slideshowButton default css for button in Overlay.