Add 'gmsh::model::mesh::getGaussPoints'

See merge request !261

Bezier coeff

See merge request !260

- document getBoundingBox when dim and tag are < 0

should be investigated further (reported by Ruth: select "3D model" for models/ElectricMachines/pmsm.geo)

- make "alignPeriodic" stuff less verbose; should this even still be called? Silently modifying the mesh
  after reading it seems like a very bad (TM) idea