Code formatting.
- Added stub for Quaternion class.
- Implemented Matrix4::model. It now returns the correct model transformation matrix.
- Added Framebuffer::Resolution enumeration. This will make it easier to select
  a framebuffer resolution from the GUI.
- Added output operators for the Framebuffer class and Framebuffer::Resolution enumeration.
- Added a combo box to change the framebuffer's resolution.
- Made GUI combo box text more readable by changing the font color from white to yellow.
- Added 8K Ultra HD (UHD) framebuffer resolution.
- Added a uint32_t conversion operator to the ColorRGBA class, which simply merges
  the RGBA object's channels and returns the resulting 32-bit unsigned integer.
- Implemented the NormalsRenderParameters.
- Added stubs for Depth, Constant, Phong, Cel, Bump and Deferred render parameters.
Code refactoring. The most important change to this version is a more versatile rendering pipeline, i.e. different stages of the pipeline can now have different implementations.
- Added an 'UpdateCompleteTask' to emit the 'updateComplete' signal of a given
  subsystem. This will be useful to know when an 'UpdateTask', created by a
  subsystem, that spawns sub-tasks has completed.
- Added a Physics subsystem.
- Added an 'UpdateTask' to all subsystems.
- Added an 'UpdateGeometryTask' to update a scene object's geometry.
- An IDE misconfiguration led to the scene/object.cpp file being saved with
  Windows line endings (CR/LF). These were reverted back to UNIX line endings (LF).
- Updated documentation for the Vertex and Viewport classes.
- Reverted back to rotation vectors from quaternions in the scene::Object
  class. Using quaternions is an implementation detail so to prevent any
  future complications, usage is left inside the Matrix4::rotate method.
- Refactored a few scene::Object's methods.
- Implemented Euclidean rotation in Matrix4::rotate. Later on, this will
  be updated to use quaternions.
- Optimised the Matrix4::inverse function to reduce calls to the
  Matrix4::get method.
- Stopped tracking 'Makefile' since it's automatically generated by qmake.