Make the responders list UI more user-friendly and useful

[azasypkin]

Summary

Today, the responders list UI is quite busy as it tries to display as much information about every responder as feasible. However, it turns out most of that information (e.g., status code and whether the responder uses a custom body or response headers) isn't that helpful to the users. Meanwhile, some more useful information is either hard to scan quickly (e.g., responder URL displayed only as the 6th field) or not available at all (e.g., last request timestamp).

The scope of this issue is to make the responders list UI more user-friendly and useful.

[azasypkin]

Handled via beb8ebe, secutils-dev/secutils-webui@bc5d202, a52821c, and secutils-dev/secutils-webui@7ec96da and deployed to Secutils Cloud.