Iceberg implemented its own MCPackage>>snapshot method to modify the one of Monticello. 

The method of Monticello was updated to use the same change as Iceberg but also it was updated to reduce the number of categories (package-tag) manipulations. I want to check here if we could use this new version for Iceberg too as a step toward getting rid of the categories in Pharo

Base the organization definition on packages and tags instead of categories.

#ensureMCClassOrganisationHasCorrectStructure: has been simplified because now the organization knows the package and we do not need to do magic to ensure we have the right one

IcePackageDefinition has been updated to use the package name and tag names instead of categories.

This change includes pharo-vcs#1728

…izationdefinition

…izationdefinition