Issue Summary

Downgrade app/plugin by uploading older jar file in 'Manage apps' should give proper error/failed message. At the moment when we upload an old jar file of existing third party app then the popup shows installing and complete and displays the current existing version.

This is reproducible on Data Center: yes

Steps to Reproduce

1. Download older version of jar file of a third party app for which a newer version already exists in confluence
2. Go to 'Manage apps' > Upload App > Choose jar file of older version of an existing third party app > Upload
3. The pop shows as Installing and complete but downgrade doesn't happen and there is no error/failure message.

Suggestion

When a downgrade is attempted for a third party app by uploading an older version of jar file, there should be pop up message or notification that says failed/error.