[FileIO] io namespace, path, misc fixes for Directory, refactor

implemented path related string parsing
fixed Directory::GetFileList
refactored io related code into the oakvr::core::io namespace
created a new namespace with path related string parsing functionality called oakvr::core::io::path
might break compilation because oakvr::Core was renamed into oakvr::core
[OakVR] refactor, MemoryBuffer, ResourceManager, OpenGL

* renamed oakvr::Core into oakvr::core
* added MemoryBuffer typedef for Buffer<uint8_t>
* refactored ResourceManager to work with MemoryBuffers instead of IResource;
* OpenGL now uses glfw instead of directly using wgl