Using nanoflann's kd-tree for fast searching

Fixed previously uninitialised screen_width/height in constructor from ScaledOrthoProjectionParameters

These changes are for the closest edge fitting.

* Function to compute the mesh contour vertices
* nanoflann adaptor for vector<Eigen::Vector2d> (it should work with glm::vec2 too actually)

Adjusted RenderingParameters constructor accordingly.

This is useful to get correct angle estimates when, as in OpenCV, the viewport is upside-down.
It could maybe also be solved by negating the 2nd and 3rd row of the rotation matrix in RenderingParameters, but I couldn't get the projection right. This is probably nicer.

It still needs a more proper cleanup.

RenderingParameters gets more and more chaotic, needs a major overhaul.

Based on the affine camera estimate, and then doing SVD to obtain the closest orthonormal rotation matrix.

This is mainly to accommodate fit-model-ceres, where I've used double for all parameters

Also removed trailing space from vertex/colour data

Changed all affected functions and classes accordingly: Mainly the renderer, affine-renderer, and affine texture extraction.

This results in a ~35% speed-up of rendering meshes.

It requires some not-so-beautiful conversions in render_affine and the current texture extraction, but they will be superseded by the new renderer soon anyway.

Not sure what's the best place to put them, let's put them here for now.

He updated it quite a few months ago and sent the file to me - now finally committed.

* Added const and non-const overloads. The non-const is needed because of the RNG in PcaModel.
* Renamed a few variables for consistency

This is needed by the json-to-cereal-binary app to read the JSON generated from the Matlab BFM converter script.

Renamed fit_shape_model to fit_shape, since it's fitting the shape in general (including blendshapes), and not only the PCA model.

I don't think we need two representations for it, one struct with a type is easier. At the moment, we only use an orthographic camera anyway.

- As before, it should contain all the parameters necessary to render an image using OpenGL, and conform to the OpenGL conventions
- Updated all calling sites
- Added serialisation
- Added a convenience method to save the parameters to a json file