feature/477: Creating Walkthrough default widget

* adding new library: reveal.js - recompiled in order to work fullscrren as we need it
* adding gulpfile for compiling sass files
* modifing iframe template to use the new library
* modifing walkthrough_slideshow module, to load slideshows when there are no screenshots
* adding new iconfonts (extending the existing ones, generated with icomoon webapp)