Moved the project into a subproject.

So we can have multiple subprojects in the future!
Added CMake command to copy resource files to binary location.
Added search paths to search for files in the same folder as the executable.
Refactored Shader object out to common folder.
Moved ResourceManager to common folder.
Added trailing slash to search_path.
Added global common config with some constants.
Added simple Model and Mesh PODs.
Added GLModel and GLMesh objects.

They are responsible for taking Models and Meshes and putting them into
graphics memory and doing fancy things with attrib pointers and such.
Created AssimpLoader to create Models and Meshes from Assimp objects.
Changed implementation to use the new GLModel and GLMesh objects.
Removed old unused Mesh and Model objects.