Change for conditionally displayed config items (based on other params), and fix for layout of some config items

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

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

from the autopilot.

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

Cleaned up MainWindow init dramatically, relying now on Qts persistence capabilities. Fixed a number of view persistence issues this way