Need ability to Rollback and Reimport User accounts

Problem/Motivation:

Some Migrations are stalled because the User Accounts have changed from the point of initial migration and if we can't rollback and reimport the user data, we can't synch the data without scrapping the migrated site and starting fresh.

Steps to reproduce:

Create a migration site and link to a site, linked to a site that has changes to its user accounts.

Proposed resolution

Add ability to Rollback and Reimport User accounts

Remaining tasks

TBD

User interface changes

Unlock the User Account item within the "Completed Migrations" listing page and/or have User Accounts as part of the "Refresh Migrations" page.

API changes

TBD

Data model changes

TBD