Changes for new calibration in APM 3.0 (Re: https://github.com/diydrones/MissionPlanner/issues/38), and change in some of the serial timeouts

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.