Resolve "[Alya] Create a new data distributor - Moves instantiation outside read/write"

Closes #88 (closed) Closes #125 (closed)

The distributor will read a shared file including [filename] [host] [size] [offset] and distribute the files accordingly. We assume, as it should happen in SLURM that the nodes are in alphabetical order.

Distributors are instantiated per read/write operation. They should be moved to FsData to avoid the overhead. It is also necessary to reduce the creation cost when the distributor reads the data mappings from a file or similar.