Fieldsplit Preconditioning: use colon-separated list to specify the blocs

[lberti]

Presently, via the function parseFieldsDef in feel/feelalg/datamap.cpp, one can only read lines of comma-separated integers, as in

0->(1,2,3,4,5,6,7,8,9,10,11),1->(1,4,7,10).

In order to simplify data insertion, one should read colon-separated integers as in

0->(1:11),1->(1:10:3),

and obtain an equivalent result as in 0->(1,2,3,4,5,6,7,8,9,10,11),1->(1,4,7,10).