* removing $graphs global
* remove unused things
* fix some additional graphs
* Fix graphs persisting too soon
* correct name for poller module performance graph
* only one type of graph is used here
* Device Availability Calculation
* Travis fix
* .
* schema corrections
* flexible duration
* travis
* .
* .
* .
* .
* remove not needed code
* line Text to RRD
* update humantime
* .
* only set up again if device was marked as down
* set RRD area transparency
* save uptime also, to keep last availability as good as possible
* file description correction
* look for outages even if uptime > duration
