Fixed valueChanged bug in QGCParamSlider and added in automatic min/max slider values based on param QVariant type

Configuration parameters are now split into two categories, General and
Advanced, where General parameters are anything defined in the
configuration file and Advanced are anything not defined in the
configuration file, but the autopilot still returns when requesting a
parameter list.

This commit still allows configuration widgets to be loaded from qgc files
assuming that there is no APM generated xml file (arduplane.pdef.xml) in
the files/%autopilorname%/ directory. This filename needs to be
configurable, and selectable at runtime. It is not yet.

APM configuration, battery and extra sensors

configuration directories