Add new hybrid step integrator for improved mass conserving cavitation model

This branch adds several improvements related to the mass conserving cavitation model of module-hydrodynamic_plain_bearing2. One of the main improvements is the new option to use the multistep solver for all structural degrees of freedom, and at the same time use crank nicolson for the fluid domain of a model involving fluid structure interaction. For some models this can reduce the total number of iterations by up to 25% and also increase the accuracy of the solution when compared to the multistep method alone.