Improved performance of the cpu widget

[atopion]

Hi,
first of all, thank you very much. Your project is amazing.

However, just like #120 I did notice a rather high cpu load of the cpu widget.
When adding this widget, my awesome process averages at 15-20 %, compared to 0-3 % when it is not added (measured with htop).

After looking into the code, I noticed that the widget is constantly parsing the output of the ps command, even when the popup is not opened (which should be the case most of the time after all).
I therefore wrote this modification, where the widget runs a different command while the popup is closed, one that only reads in the first cpu line of /proc/stat and parses it. When the popup is opened, the other command is run, while it is open, so there is no loss of functionality.
The only caveat is, that this modification is increasing the opening time of the popup a little bit, but this is barely noticeable.

With this new modification, I was able to get the cpu load of the awesome process down to about 2-3.5 % while the popup is closed (again measured with htop).

Kind regards.

[streetturtle]

This is super cool! Thank you very much 👍