SoftwareUpdater: Make updates more robust (restart package downloads)

[stippi]

I tried to perform an update yesterday and since there are many packages to update, there seems to be an increased chance of a package failing to download fully. On my first attempt, the "haiku_x86" package failed, on my second attempt, some qt package. I don't know if already downloaded packages are at least cached, but it seems unnecessary that I need to manually restart the update process. SoftwareUpdater could at least try 3 times for the same given package without any intervention. Then it could continue to download other packages. And when there are finally only "failed" packages left and the installation of the successful packages is impossible due to this, there could be a prompt, and the prompt should contain a "Retry" button.

It would also be nice, but I don't know if our infrastructure makes this possible, if partial downloads could be continued. That would probably get rid of most unnecessary traffic. Binary diffs would of course be even better... but that is left for another ticket. :-)

[diver]

Looks like a dupe of #12414.

[stippi]

I agree, but SoftwareUpdater still needs at least a "Retry" button. And depending on how much and where some of the functionality is located, some of the other points may also be relevant to SoftwareUpdater as well.

The biggest bummer is that already downloaded packages are downloaded again.

[pulkomandy]

This is indeed a duplicate of #12414.