UI does not show if a migration needs reset

Problem/Motivation

If a migration has failed before or was interrupted, it needs a reset before it can run again.
(or maybe sometimes just a "stop"? not sure)

However, in the migrate_tools UI at admin/structure/migrate/manage/GROUP/migrations/MIGRATION/execute, there is no indication that a reset is needed.

In fact, when running the "Import", ist just seems to run the migration as if nothing is wrong, and then reports 0 rows.

Steps to reproduce

Proposed resolution

Report the migration status at the top of the "Execute" page.
If a reset or stop is needed, disable the "Import" option.

Or alternatively, provide an option to do the stop + reset as part of the import.

Remaining tasks

User interface changes

API changes

Data model changes