Lights oriented the wrong way

[CHILLYBUS]

This is the 'lights are pointed some different direction' weirdness that happens from time to time. Not sure how to replicate, but it 's fixed by grabbing the whole level and spinning it on each axis a couple of times.

[arbruijn]

OffAngle_Light_issue_fi.zip Test level from Fisholith on Discord

My analysis from Discord:
The editor uses the OpenTK library, which has this code for converting a rotation matrix to a rotation quaternion as used by unity: https://github.com/opentk/opentk/blob/develop/src/OpenTK/Math/Matrix4.cs#LC453
This code does the wrong thing if the trace is just slightly above 0, which of course easily happens with float math. The blender code where this was apparently copied from has a margin of 1e-4 here: https://github.com/dfelinto/blender/blob/eb6fe5fa94b86a0a20742e06bf1e68b4cbaf6693/source/blender/blenlib/intern/math_rotation.c#L295
This page has more explanation and a slightly different algorithm which might be even more stable, but it also seems to use a different orientation: http://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToQuaternion/index.htm

I've created a pull request to use the modified version of the OpenTK function when exporting lights: #32