Independent scale for upload/download limits

[Bilge]

Some Internet connections have unequal upload and download capacities. Typically the upload cap is less than that of the download. In such configurations, the upload bar will never reach the same height as the download because they share the same scale. Generally it makes sense for them to share the same scale since they remain proportional to each other, but some users might prefer unlinked scales such that both streams can utilize the full height of the graph.

It might be worth implementing this separately for the graph and the tray icon meters such that this feature can be toggled independently for both.

Alternatively it might suffice to just add a second peak line.