Thermal plotting additions
Created by: valschneider
This PR is about:
- Changing the drawstyle of plotting methods to 'steps-post'
- Adding cdev_state plotting methods for devfreq and cpufreq cooling devices.
- Adding xlim/ylim parameters to new and existing plotting methods (mostly to help in my next LISA PR)
This is what the plots look like: https://gist.github.com/valschneider/81a247b6acb69cccfe6e0ad7682914a8#file-thermal_plotting-ipynb