add information about other e-items of the same provider

[kpsherva]

On the import time (or delete) e-items are matched by the creator value (in this case provider, value is inserted on import time), see
https://github.com/CERNDocumentServer/cds-ils/blob/master/cds_ils/importer/eitems/api.py#L15
this workflow won't work if the e-item was created manually by the librarian - leading to duplications and not deleted e-items. We want to avoid using "source" field of the e-item to match them due to possible human errors while editing this field.
Instead we should add an information in the report stating that another e-item of the currently processed provider was detected and manual action is required.
The information should be visible in "Actions and details" as well as the row should be highlighted in yellow