Pass the context object to plugins implementing the IPackageController and IGroupController

[amercader]

Plugins implementing some IPackageController or IGroupController operations (i.e. read, create, edit, delete) may need the context used in the logic action. For instance, to access the Session that created a package to perform additional queries from the extension (In that case the main logic action will still perform the final commit). The interface methods will have a default value of None for the context to ensure backwards-compatibility.