Add per-manga preferred viewer

[Thomas Harning]

A useful feature to make the best use of the current viewers would be to have the option to set the default choice for viewer per-manga.

In strip-style comics (ex: The Gamer) the 'simple' viewer works great because the simple viewer fits-to-width and the comic reads from top-down quite smoothly.

Most comics, however, I prefer to read using the pager.

Currently I use the 'Choice Dialog' for the viewer type options as it lets me pick the 'simple' viewer when I need it and the others for then... but it'd be nice to set a 'default' preference in the global configuration and allow for the viewer to be set per-item.

[cylonu87]

v4.0.0-5

[Thomas Harning]

Confirmed as working for bookmarks, does not work for downloaded ones (though given the disconnect between what has been downloaded and what is in the live bookmarks, it is understandable).