Downloads message bar screenshots

Screenshots for the new strings in !111 (merged).

screenshots/tor-downloads-message-bar-library.png, screenshots/tor-downloads-message-bar-panel.png and screenshots/tor-downloads-message-bar-panel.png are all for:

• downloads-tor-warning-message-bar
• downloads-tor-warning-tails-link
• downloads-tor-warning-dismiss-button. Note this string should stop using the old screenshots tor-downloads-warning-library.png, tor-downloads-warning-page.png, tor-downloads-warning-panel.png and use the new ones in their place.

NOTE: The old screenshots tor-downloads-warning-library.png, tor-downloads-warning-page.png, tor-downloads-warning-panel.png should still be used for the 13.5 strings downloads-tor-warning-title and downloads-tor-warning-description. But after 14.0 is stable and the strings are removed from weblate, we can delete those files.