Only add 'group_name' if sourced from Wizard

Problem/Motivation

I like the improvements added with wizard, however, there isn't any way to export the wizard config via ctools. And I generally prefer to build my own migration registrations anyway. So I ended up rolling my own hook_migrate_api(). Problem: wordpress_migrate assumes that all Migration names include the 'group_name' as a prefix. I have a bunch of migrations on this site from various sources. None of the others are prefixed with the group name.

Proposed resolution

Set a flag in the wizard and only hard-code add the prefixed group name if this is sourced from the wizard. Give full control back to folks who aren't using the wizard. The hardest area to do this in complete() for attachments. It makes a lot of strong assumptions about migration naming. That logic should be cleaned up and simplified.

Remaining tasks

Write a patch.

User interface changes

n/a

API changes

n/a

Data model changes

n/a