Add admin option to enable/disable compression when archiving task directories

[prioux]

Right now we always run tar -czf ; I'd like an option such that in particular cases, I can create a tar archive that is not compressed (tar -cf).

The CbrainTask's model code need to be able to figure out whether to use compression or not when de-archiving too (using the extension .gz on the archive file for instance)

[MontrealSergiy]

seems resolved

[prioux]

This is not resolved. The feature is not yet implemented.