Add grpc endpoints providing system information

[MalteJ]

Add grpc endpoints that can be used to inspect the system state:

• Memory usage
• CPU usage
• Load
• Uptime
• Process list
• Disk stats
• Disks' SMART information
• Network stats
• Temperatures
• Fans
• List of PCI devices

[lukasfrank]

Partially implemented:

FeOS/proto/feos.proto

Lines 61 to 67 in c8a05d5

	message HostInfoResponse {
	uint64 uptime = 1;
	uint64 ram_total = 2;
	uint64 ram_unused = 3;
	uint64 num_cores = 4;
	repeated NetInterface net_interfaces = 5;
	}