Improve workspace management

Workspaces as TT,TS matrices could have a lower memory footprint, if we change the descriptors in the case of StarPU for descriptor without data, that will be allocated at first use.

mentioned in merge request !54 (merged)

changed milestone to %Chameleon 1.1.0

Fixed by !140 (merged)

changed milestone to %Chameleon 0.9.2

closed