File view.

I guess this is in a mergeable state.

New things:

* The view allows you to select which file to not download, but beware, they are still allocated on the file system
* Double click on a file / folder opens said file / folder
* Can set priorities on a per-file basis, or apply it to a whole folder, or with your selection (shift/ctrl + leftclick)
* Displays file icons as the file are allocated, uses a stub instead.

Fixes:

* At a point, the multiple selection in the torrent treeview was disabled, so it's re-enabled in this branch.