- wrap request in AnkiRequestsClient so we can keep track of
upload/download bytes without having to monkey patch anything
- force a 64kB buffer size instead of the default 8kB
- show one decimal point in up/down so small requests still give
visual feedback
- update add-on downloading and update check to use requests
- remove the update throttling in aqt/sync.py, as it's not really
necessary anymore
