Changed the second pressure correction to an optional step, which can be changed by applying the time_stepping_method-parameter
Commit for Run 2
 Commit for Run 1
Commit for Run 1
Commit for Run 3
Added the possibility of having the final pressure correction only before the ouput of the solution. Also removed some redundant variables to the final_pressure_corrector
Commit for Run 2
Commit for Run 1
Removed the pressure term from the predictor, by setting the pressure and momentum_source_terms to 0
Commit for Run 3. Run 2 is skipped, because compared with Run 1 only the initial condition for the pressure is different. The difference in inital condition is not used in the simulation.