Addition of new "User" param for apm.pdef.xml file, allowing for sorting config entries between general and advanced tabs

Variable calibration procedure text based on the autopilot, stored in files/%autopilot%/general/calibration/description.txt.
Added a new QGCTextLabel type for QGW files, which can display MAV text or hardcoded text.
Added tabular configuration screens based on folder structure inside the files/autopilot/airframe folders

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

added Rascal airplane model for flightgear which also includes a 3D model (from http://flightgear.org/legacy-Downloads/aircraft-2.0.0/)

Addressed issue #26. Select System, Plugins and System are disabled when neccessary. Removed style-outdoor-dark.css. Moved the other two .css files and Vera.ttf into files/styles.

Added a mavgen.exe file which converts the xml into the header files. Only mavlink v1.0 is tested so far. the fixed headers in files/mavlink_generator/C should always be updated to the newest versions.