Correctly handle failed downloads

[dromzeh]

When downloading multiple files, there is a random possibility where some files fail to download.

Failed downloads should be correctly handled by storing the failed downloads - after the download of the remaining files, the failed files should attempt to re-download.

In the case that this still errors, there should be suitable error logging & inform that certain files failed to download (including which ones(?))

There should also be a popup window dependent on users UA to prevent unnecessary downloads in the first place which are bound to error.

[dromzeh]

will probably set UA popup window to display before each download, with the option to not see the message again - handle failed downloads w/ a reusable random component for errors

maybe re-implement sentry with as little tracking as possible, create uuids for rare errors that occur when downloading all/multiple and give users the option to report them that way