using olwJumbotronDirective to define the layout of the landing page
added use of olwLi[Body]Directive
major change: getSources+getChapters now defer a promise. getSources HEAD-requests all possible files, returns urls of the files that are acutally available in cdn. #90
adapted to the new promise from olwCdnService. chapter links not working atm, i'm on it.
chapter links work again. needed to wait for the sources to watch the main type.