Load P3D 64 bit SimConnect shared library at runtime

This aligns the behavior and concept with the 32 bit FSX version. SimConnect
is loaded at runtime, depending on the version being selected.
It also adds a featuren to change the P3D SimConnect version at runtime by
unloading the previous and loading a new one.

ref T349

src/blackconfig/buildconfig.h

@@ -147,9 +147,6 @@ namespace BlackConfig
         //! \returns 32, 64 or -1 (in case no info is possible)
         static int buildWordSize();
 
-        //! P3D 64 bit build version
-        static const QString &p3dX64BuildVersion(); // defined in buildconfig_gen.cpp.in
-
     private:
         //! Major version
         static int versionMajor(); // defined in buildconfig_gen.cpp.in