* added support form yaml-cpp >= 5.0.1

* when yaml-cpp < 5.0.0 define OLDYAML
* added yaml-cpp 5.0.1 tarball in preparation for moving to the new api
* added OCIOYaml class and moved all yaml-cpp code into OCIOYaml.cpp
* moved Config serialize code into OCIOYaml.cpp
* added Config::setEnvironmentMode(), Config::getEnvironmentMode(), Config::loadEnvironment()
* moved Display code from Config.cpp into it's own files