Update the methods of the FunctorCollection tool (FunTuple)

This merge request addresses some of the comments provided during the 23rd LHCb hackathon, as discussed in #15 (closed) . As we want the FunctorCollection tool to behave like a smart python dictionary with the same methods, the following replacements have taken place:

• FunctorCollection.extend becomes FunctorCollection.update
• FunctorCollection.remove becomes FunctorCollection.pop

The option file has been updated accordingly.

FYI @amathad @powen

This MR closes issue #15 (closed) .