ENH: finiteArea: new models for shallow film modelling

- new model framework: liquidFilm
- new film turbulence models: filmTurbulenceModel with friction models
- new velocity boundary condition: velocityFilmShell to handle/evolve regionFa film
- new function object: setTimeStep to control the simulation time-step based on regionFa Courant number
- add support for the absorption of Lagrangian particles into films