Even once TwoColConflict is the default conflict workflow for a wiki, it should still be possible for individual users to choose to continue using the old workflow.
- Create a new user preference in the Editing tab, which determines which conflict workflow will be used.
- Preference defaults to TwoColConflict
- Preference is only visible when TwoColConflict is configured as the default, and is invisible when configured as a beta feature.
- If the user has opted out of the beta feature, transfer that over to the opt-out user preference.
- Include browser tests.