Added a very inefficient way to browse transparently read all comics in a directory by generating a list of files in the directory, searching for the file, and then selecting the index+1 or -1 filename.  This should surely be improved in teh future but for now this is sufficient for my purposes.

Made it so that when a renderwidget goes beyond the number of pages available it displays a 1-pixel black image (which turns into the whole widget for now because of the black background).