Fix #1035: Do not override the pkgconfig path, append instead

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
fix #1036: add Eigen include directory to the exported cflags

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
cmake: tests should not end up in bin dir

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
use doubles instead of floats for quaternion calculation

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
fix #1036: implemented more robust version of GetRotAngle, it uses a conversion to quaternions under the hood

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
merging changes from upstream