Add new module hydrodynamic_plain_bearing2

This branch adds a new user defined element for hydrodynamic plain bearings based on a direct solution of the Reynolds equation. That element supports advanced features like journal- and shell-elasticity, arbitrary lubrication grooves, non-cylindrical bearing shapes, mass conserving cavitation, asperity contact, hydrodynamic- and Coulomb-friction, and also an energy conserving 2D thermal model.