[v6r10] [NEW] Porting wf from lhcb

From https://github.com/DIRACGrid/DIRAC/pull/1586, I applied some fixes taking into account the comments, and added very few things. The notes to the previous one are still valid (for the "what's new? How to update")

For what regards the connected inputs: I decided to leave what I coded before, i.e. I just changed from "gaudiSteps" to "appSteps", because I remembered why I changed to this way long time ago in LHCb. The reason is that I prefer not having special parameters: instead, the parameters are now created all in the same way (so, no links) and the choices are made only depending on the content of the parameters values. Anyway, this do not prevent anyone from adding also the possibility to recognize links, especially for this case.