Add integrity checking of downloaded packages and a GitLab mirror #5
Description
As an improvement, BatCenter needs a way to check the integrity of the downloaded packages in order to make sure that they haven't been altered during the data transfer, avoiding possible malware interceptions.
To ensure that BatCenter is up 100% of the times, having a mirror would definitely help. This way, if a file had got corrupted, the program should try to download a copy from the other mirror.