Fixed camera scale movement due to DEG->RAD change

Fixed camera scale movement due to DEG->RAD change when upgrading GLM
    src/ui/CameraFpv.cpp
Added rudimentary resource manager

Added rudimentary resource manager
    src/core/MainManager.cpp
    src/core/MainManager.h
    src/io/ResourceManager.cpp   (+)
    src/io/ResourceManager.h     (+)
    src/io/TestResourceManager.h (+)
Added simplified resource loader function

Added simplified resource loader function
    src/io/ResourceManager.cpp
    src/io/ResourceManager.h
    src/io/TestResourceManager.h
Simplified ResourceManager access from MainManager

Simplified ResourceManager access from MainManager
    src/core/MainManager.cpp
    src/core/MainManager.h
MeshRender now uses ResourceManager
    src/ui/MeshRender.cpp
    src/ui/MeshRender.h
    src/wip/DeferredRenderer.cpp
    src/wip/DeferredRenderer.h
Added empty constructor to Asset

Added empty constructor to Asset
    src/util/Asset.cpp
    src/util/Asset.h
    src/util/TestAsset.h
Added shorthand loadShader to ResourceManager

Added shorthand loadShader to ResourceManager, similar to load{Shader,Image}
    src/io/ResourceManager.cpp
    src/io/ResourceManager.h
    src/ui/Surface.cpp
    src/ui/Surface.h
Increased use of ResourceManager

Increased use of ResourceManager
    src/wip/DeferredRenderer.cpp
    src/wip/DeferredRenderer.h