Add Trackers from a URL list

[teddyrogers]

Feature request, when adding a tracker, instead of accepting only individual tracker URL's allow adding a compiled list from a link, e.g.

https://raw.githubusercontent.com/ngosang/trackerslist/master/trackers_all.txt

qBittorrent has something similar and is able to download a µTorrent compatible list and add the trackers from the list.

It would also be good if the URL trackers list was made permanent (available) to add even after closing and restarting Tribler, without manually copy pasting the URL each time.

Having the URL list available to add (either manually or automatically) whilst importing new torrents would also be great.

[qstokkink]

Thanks for the suggestion! I think we can look at this for 8.1.0.