Add horizontal scrollbar to System Information graphs

[SanderBouwhuis]

Currently, how far back in history you can see changes depends on how large you make the window. So, someone with a large screen can see more than someone with a small screen. That is ridiculous!

Here is an example for the Memory tab, but it holds for all tabs/graphs.

A small window (look back a tiny bit):

A large window (look back quite far):

Please add a horizontal scrollbar so that we can always look back.