Suspend/resume feature development

Goal is to implement #256 (closed). Tasks:

• Implement a temperature model for bad/old devices
• Prevent actions while device is hot according to model
• Add "critical" sections
• Add suspend/resume vfuncs
• Add feature flag for suspend/resume
• Add public suspend/resume API

And tests …

Questions:

• The temperature model right now is exponential. Maybe it should just be linear to make it simpler?