Added throttling reasons and cpu uptime

[gerth2]

While doing some debugging last night, I had a number of issues with my power supply on the Pi. When I hooked up a keyboard and screen manually I quickly found root cause due to the messages in the console from the kernel, but I wasn't seeing these show up anywhere else in an obvious fashion.

The symptoms actually align some ancedotal reports from @dkt01 of settings not saving and recalling - if a reboot had happened on or during the settings write, it could cause intermittent issues.

I added Raspberry-Pi specific throttling reason and CPU uptime metrics to the Settings/General tab to help identify this as root cause.