Feature/interp point cloud processing

First integration of salome_script interpolate feature.

Options supported :

--varname
--varunit
--kind
--shift-x
--shift-y
--zone
--default-value

Waiting for EDF informations for other options :

--chunk-interp
--blockpts, 
--outside-zone
--chunk-interp 
--chunk-x-partitions
--chunk-y-partitions
--chunk-overlap
--mmap
--record (default -1)

Refactoring of variable related code with introduction of VariablesUtils class