[simulations] Allow to set source density and catalog the same time (sampling)...

[simulations] Allow to set source density and catalog the same time (sampling) + allow n_src=0 for only background simulation
5 jobs for master in 5 minutes and 21 seconds (queued for 3 seconds)
Name Stage Failure
failed
Unittest35 Unittest There is an unknown failure, please try again
FAILED (errors=2)
Warning: the same energies have been used for all simulated sets (nsets).
Warning: No extragalactic smearing of the sources performed before lensing (smear_sources). Sources are considered point-like.
Warning: No extragalactic smearing of the sources performed before lensing (smear_sources). Sources are considered point-like.
Warning: not enough sources. Set keyword 'n_src' (currently 100) higher?
Warning: not enough sources. Set keyword 'n_src' (currently 100) higher?
No explicit sources have been set!
Warning: not enough sources. Set keyword 'n_src' (currently 0) higher?
No explicit sources have been set!
No explicit sources have been set!
failed
Unittest27 Unittest There is an unknown failure, please try again

----------------------------------------------------------------------
Ran 38 tests in 3.892s

FAILED (failures=1, skipped=11)
Warning: the same energies have been used for all simulated sets (nsets).
Warning: No extragalactic smearing of the sources performed before lensing (smear_sources). Sources are considered point-like.
Warning: No extragalactic smearing of the sources performed before lensing (smear_sources). Sources are considered point-like.
No explicit sources have been set!
No explicit sources have been set!