Rename HdyPaginator into HdyCarousel
WIP because I'd like to know: should we deprecate
HdyPaginator and add
HdyCarousel in 0.0 first? Then it would smooth the migration out for our users and we wouldn't need to document the migration, as it would be handled by the "Do not use deprecated symbols" section.
CC @guido.gunther @exalm