Add generic translate icon, symlink crow-translate-tray

The crow-translate icon has a systray icon variant that works as a generic translate action icon we don't have yet. This symlinks the old crow-translate-tray to this now generic "translate" icon.

Reasoning

We don't have a generic "translation" icon or anything yet, the only thing existing is this "crow-translate-tray" icon. However to me it looks suitably generic and I would love to use it in places such as Ruqola's preferences or the possible Tokodon translate feature:

How it looks in Cuttlefish now: