0024188: Update issue history code to display user names via standard APIs - MantisBT

When preparing a username for display, use prepare_user_name(). Feel free to add an argument to express if you want it in text vs. html, but the business logic for formatting a user name should be captured in one place. We should also consider having history_get_event_from_row() take an argument for html vs. text and pass it to prepare_user_name(), so the right format happens for html with tooltip, class name, etc vs. text email.

This is follow up change to the following PR:
https://github.com/mantisbt/mantisbt/pull/1321