Changed dependecy to webkit-1.0,added web view to window properties

Currently the backend/epub/epub-document.c file has some dummy code, such as that for thumbnails, solely to get it to build. Now that we are done with all functions
that we would possibly need to handle the backend, I am now working now on displaying the document via a webview, starting with this commit where i add a webview to the EvWindow properties. Similar to this I need to put in custom functions for epub, as rendering is done by the layout engine. I will also need to add some epub specific callback functions to the widgets.