Replace 9 seperate valueChanged() signals with just 1, and remove the resultant tons of code duplication

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

Fixed roll angle in Google earth, still not smooth. Fixed a number of threading issues. Fixed all custom widget related bugs. Improved MAVLink decoder. Reduced CPU usage substantially across all views

Started parameter interface refactoring to adhere to MVC design pattern. Working on getting custom widgets completely up and running