Add rush larsen scheme to multistage solver
Add non working test for RL1
Add Rush Larsen and Generalized Rush Larsen as time stepping scheme to the PointIntegralSolver
Added second order Rush Larsen solver schemes.
 -- Splitted all rush larsen logics into a its own module
Merge branch 'johanhake/multistage-rush-larsen'
Add copyright statement
Merge branch 'johanhake/multistage-rush-larsen'