Major improvements

ADDED:
 - generic class "system_stats" that will read all different system
commands
 - function to detect the system editor (will be needed later)
 - function to get the file path of the config file
 - accepts —config or -c command line parameter (not doing anything
yet; compare #8)
 - check if there is an instance of serverstatus running already

CHANGED:
 - serverstatus.cpp now calls 5 times SystemStats with the different
paramteres (cpu, load, hdd, mount, memory)

DELETED:
 - all specified files cpu, hdd and memory (cpp and h)

FIXED:
 - closed #7: generic file decreases compiled file size of more than 20
percents