Remove deprecated project kwarg in Cluster implementation, or use it as it should be

[guillaumeeb]

Initially, project kwarg was used in PBS, SGE and SLURM Cluster implementations to position the account (or -A) options of each job scheduler. As there is also a real project option in some of them, it has been renamed to account, but the previous kwarg was kept for backward compatibility with a Warning.

It is now time either to remove completly the kwarg there, or use it correctly for what it means in each HPC Scheduler glossary.

See #586 for history.