Port free flow tests to new staggered

Tests should be ported one by one in separate merge requests. In principle, the new implementations are available in !2201 (closed). Move changes from problem_new.hh and main_new.hh to problem.hh, main.hhand properties.hh. Be careful as !2201 (closed) is already partly outdated. !2830 (merged) is a port based on the current master.

• navierstokes/angeli: @heck
• navierstokes/channel/1d: @RoWin
• navierstokes/channel/pipe: @hanchuan
• examples/liddrivencavity: @nedc