Thumbnails for Epub Documents

This commit is mainly so that any further changes can be reverted to this state. The thumbnails are of very large sizes so I need to fix that, and in general implement thumbnails. Also I am facing an X-windows error, which I can't seem to fix. I feel it may be a problem with webkit-1.0, so will try the build with gtk3 and webkit2. If so is the case, I'll have to work something out for that. Should be able to push a commit soon where the document can actually be read, soon as I figure out the perfect place for the call to load uri.

Other than that more function were modified in accordance with webkit. The error I get when opening the file from the filechooser still persists, I need to fix that too.