Changed the way APMPlanner2 handles looking for support files to be more...

Program can now handle the support files being in ../share/APMPlanner2 on Linux. A number of changes were required throughout the program to point to a single routine in configuration.h <QGC::shareDirectory()>, whose purpose is to return the location of the support files.

This way Linux won't need hacky shortcuts in the /bin directory, making the installation process easier/safer.

It seems that the merge from qgroundcontrol last week "Cleaned up build files (inline with QGC changes 34c2c3d980)" inadvertently removed some of my build changes from two weeks ago, by unincluding qgroundcontrol.pri in the build process. I've put those changes in QGCSetup.pri instead.