@nexedi I created this MR to make sure that we really want to have WorkingCopy and VCS-related modules in erp5_forge and not erp5_base. To me it makes more sense like this because the rest of the code is already there and it's not required at all. All Unit Tests pass with this commit.

isVcsType(), called to conditionally display VCS tab on Business Template view, will return None if erp5_forge is not installed. For the few other cases where getVcsTool() is called, it will just raise a RuntimeError stating that erp5_forge should be installed when imports of WorkingCopy fails.