Euler: Fix matrix orientation in euler matrix (de)composition

[alexlarsson]

The euler_to_matrix and matrix_to_euler code is based on:

https://github.com/matthew-brett/transforms3d/blob/master/transforms3d/euler.py

This is num-py and has the same row-major matrixes like graphene. However
that code is based on column vectors being multiplied with the matrix on
the left:

This module implements intrinsic and extrinsic axes, with standard conventions
for axes i, j, k. We assume that the matrix should be applied on the
left of the vector, and right-handed coordinate systems. To get the matrix to
apply on the right of the vector, you need the transpose of the matrix we
supply here, by the matrix transpose rule: $(M . V)^T = V^T M^T$.

To do the transpose we just change the matrix indexing macro (M) to swap
the row/column.