Dr panel fixes

Going to merge this myself since it is minor changes that shouldn't impact the functionality. Below are the main changes I made for the sake of documenting them: 

1) Updated which fields were required in the panel and changed formatting of email so that when optional fields are empty they don't appear in the email that gets sent
2) Updated the project overview and task description to html_safe so that when html is included in either of those fields, it is rendered properly in the email that gets sent rather than showing up as html syntax
3) Changed the panel filters so that it only lists unique emails (i.e. no duplicates) since the same person might appear on a panel multiple times but we don't want them to get the same email multiple times (especially if emails are sent to everyone on all panels)