cherrypick() : Add a 'All' option for the tags selection argument
As discussed with Stephanne (A) last Friday (2021-07-16) we think it would be a good (and practical) thing to have a 'Select all the equations in the (sub)model it is invoqued on' option for cherrypick()'s third argument.
Use case: in a situation where we are aggregating a big model from several sub-models scripts, for sub-models where all the equations join the aggregated model, we wouldn't have to manually write the tags list of all the equations in the submodel for cherrypick to take them all. We would instead just have to write 'All'.