Forgot to specify the dummy texture in one spot.
Changes to cmake files.
Changed the implementation model of TextRenderer.
Added Event interface and fixed up Updater interface.
Removed useless includes.
Hide FreeType completely inside FreeTypeFontLibrary.cpp.
Used PIMPL to require the definition of Math::Vector2 only in FontString.cpp.
Forward declare Color in Image.
Forward declare Image in Renderer.
Hid implementation of TextRenderer with PIMPL.
Hide use of OpenGL inside OpenGLRenderer.cpp
Removed the test program from the repository.
Minor rearranging of headers.