Update of lagrangian code, shyelab, shyplot and documentation

[cferrarin]

Several changes to upgrade the lagrangian code to the last SHYFEM version:

• new data structure
• vertical diffusion included
• lagrangian output in shyfem format
• release of particles from areas, selected times and location, initial distribution from lgr file, boundary
• wind drift and drifter inertia included
• ...

shyelab now also handles lagrangian files providing general statistics, mean trajectory, particle density shyplot now also handles lagrangian files and plots also mean trajectory documentation updated

[georgu]

Please base this pull request on the last version. If possible, can you divide the pull request in some smaller pieces, like only lagrangian, plotting, etc...