Added render registry; a singleton container 4-tuple of opengl buffer,...

Added render registry; a singleton container 4-tuple of opengl buffer, texture, program and vertex arrays.

library/phx/render_registry.hpp

+//------------------------------------------------------------------------------
+// Project Phoenix
+//
+// Copyright (c) 2017-2018 RWTH Aachen University, Germany,
+// Virtual Reality & Immersive Visualization Group.
+//------------------------------------------------------------------------------
+//                                 License
+//
+// Licensed under the 3-Clause BSD License (the "License");
+// you may not use this file except in compliance with the License.
+// See the file LICENSE for the full text.
+// You may obtain a copy of the License at
+//
+//     https://opensource.org/licenses/BSD-3-Clause
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//------------------------------------------------------------------------------
+
+#ifndef LIBRARY_PHX_RENDER_REGISTRY_HPP_
+#define LIBRARY_PHX_RENDER_REGISTRY_HPP_
+
+#include <gl/buffer.hpp>
+#include <gl/program.hpp>
+#include <gl/texture.hpp>
+#include <gl/vertex_array.hpp>
+
+#include <phx/container_tuple.hpp>
+#include <phx/singleton.hpp>
+
+namespace phx {
+class RenderRegistry : public singleton<RenderRegistry>,
+                       public ContainerTuple<gl::buffer, gl::texture_2d,
+                                             gl::program, gl::vertex_array> {};
+}  // namespace phx
+#endif  // LIBRARY_PHX_RENDER_REGISTRY_HPP_