Support for more commands for explicit fs operations

[splitice]

Sometimes you want only to work on a partial copy of the filesystem and perform one simple operation. For example to add / update a single file.

For this reason I think there should be a specific command, say s4 fs push target file_path this would upload / overwrite the file without any conflict handling (explicit upload). A CAS type upload could also be possible given a hash etc.

There should probably be specific pull command, rename command etc.