Automation up to DL3

[morcuended]

DL1b -> DL2 (a matter of choosing the proper RF model in the grid NSB x declination):

• Decide whether to merge at DL1b or DL2 level
• cta-observatory/cta-lstchain#1296
• #280 (to avoid accessing too much the MongoDB)
• Get NSB level from DL1

DL2 -> DL3 (IRFs produced with 70% efficiency in gammaness and theta should be already produced):

• Allow for changing from subrun-wise to run-wise in the job submission scheme
• Look for the adequate IRFs folder
• Add the of DL3 file creation tool job submission