horizontal meter for states
fuddling with height
added StateMeter to GUI
better error when psutil fails to import
use StateMeter in gui
better height-handling in StateMeter
compat with older python-psutil

seems like psutil.phymem_usage() is not available on the psutil package on the beaglebone.
note that the percentage we calculate is totally different from the one returned by phymem_usage()
update SystemHealth every 2secs