Issue #1164530 Add messaging system to the content migration process. Display messages on the migration page so users can see, before the migration, what changes will be made to each field and.

Issue #1039466 Make sure number migration code does not break when migrating a field that has a custom number formatter.

Did some clean up of the List test and reverted the code that tried to check the module name for formatters, because it doesn't work.

#781088 Reorganize Content Migrate files for efficiency, and also to make it easier to use the individual module code as examples on how to implement the hooks.