Fix the HTML markup in the error message.

Problem/Motivation

The error message is currently displaying the '
' tag as raw text, and we also require a more appropriate method for rendering the array values in the error message.

Steps to reproduce

Install the module and upload a file that will cause a validation error, for example, an entry with the same URL destination as the source. Observe the error message.

Proposed resolution

Proper markup usage and tabular view of array data.

Remaining tasks

User interface changes

API changes

Data model changes