Documentation page and tutorial for FMM class

- a documentation page 
- a tutorial 
- exampleFMM2D and exampleFMM3D have been simplified. 
Good Excercice, 
I suggest to add some precision to facilitate the exercice for non common DGtal user: (even it can be logic):
- "predicate with the domain predicate." -> "predicate with the domain predicate (form the class DomainPredicate)."
- "... to combine this point predicate with the domain predicate" -> "... to combine this point predicate with the domain predicate (you will need to use the AndBoolFct2 from BasicBoolFunctions class or directly the andBF2 function)"