Download statistics

[ngld]

Track average download speed for each of the different servers and possibly country. This should help us figure out how fast downloads are for most users and if we need to improve it (and where) or if it's fine as is.

We might also want to track mod installations (though we need to figure out how to avoid duplicates even for users who aren't logged in). Storing past installations (i.e. a list of mod IDs) in the local settings should be enough to avoid counting a single installation twice (due to updates or reinstallations).