Chunk Mode for file transfer

[cheme]

Chunk mode : for big content : return a table of chunks (a cache of those should be in filekvstore and/or in filekeyval), then other query with chunk mode addressing specific chunk . Need parameterized over chunk size and chunk check hash type.

Mode is already defined in code.

This evo is nice, but should use external lib, or existing transport (ftp) for this, the point is it is rather fun thing to do.