Basic threaded downloads -might- be working now.
Changes:
- Made DownloadThread's out_queue.get explicitly non-blocking.
- Finished first version of GTK timeout callback, seems to work.
- Updated DownloadThread. Should create a file only upon successful
urlopen. Should also automatically create the necessary folder if
not present. (Maybe this should be explicit rather than automatic?)
- Made both download dialogs take a reference to the app object... I'm
still undecided whether it's better to have it included in all
relevant objects explicitly, or whether it should be made a global
ref which is imported as needed...