#376 Switch to GNUInstallDirs

[Rich Mattes]

The architecture detection logic in FindOS.cmake for automatically installing to lib or lib64 is hacky and bad, especially as new 64 bit architectures pop up. The installation paths for Player should be set using CMake's GNUInstallDirs.cmake, which contains sane defaults, allows for overriding, and tends to pick the correct architecture specific paths on its own.