Fixed library interface not compiling out of the box

This pull request fixes two issues that prevents the library interface from compiling. First, commit  938dd4cc replaced elx::Timer with itk::TimeProbe but failed to update elastixlib.h/cxx and transformixlib.h/cxx. This pull request ports the adaptations from the command line applications to the library interface. Second, gcc and g++ compiler needs -fPIC flag to be set in order to compile shared libraries. This pull request automatically sets the flag if needed.