implement niceness in all processes

[k323r]

Some services are more important than others, e.g., it is of paramount importance, that the imu measurements are always processed with as little jitter as possible. The nice value of a unix process helps the operating system to schedule the execution of the services accordingly.

[k323r]

with the current amount of services, niceness, specifically into the not-realtime services, such as dew, gps and status might be a good idea at least for single core systems.