Basic support for `clicktransition` option
Revert "Added basic support for having multiple images on the same slide"

This reverts commit cc4553909e3a2b1454d2d145c72787d7ef9886db.
Merge & conflicts
Fine-tune of `clicktransition` behaviour.
Now fotorama shows only first raw slide while initialization. Class `.fotorama--unobtrusive` makes fotorama unobtrusive and shows all raw slides, use it when you care about users without JavaScript.