Qt: Add __str__ to _DownloadWork

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Qt: Basic downloading in download_manager

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Add total segment count to progress callback

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Qt: Connect download_manager to downloads table (very basic)

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Qt: pep8

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Qt: Fix small bug in download table

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Qt: Connect progress bar in downloads table

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>