Qt: move tree header titles to class
Qt: set tree columns to Title, Network and Ep. #
Qt: add dialog to choose download bitrate
Qt: Hide previous thumbnail when we need to fetch one

Otherwise, the thumbnail of the previously selected episode shows up until the
new thumbnail is done downloading.

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Qt: download manager draft
Merge branch 'v2-qt-dev' of https://github.com/eepp/pytoutv into v2-qt-dev
Qt: Column count based on length of header data

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
toutv: Extract thumbnail caching from bos

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