Setup: add messages, set password via link

Also changed some section names to use "messages" instead of "emails".
Since I haven't added Discord/Telegram/Matrix bot setup, I mentioned you
can do these later and linked to the setup guides. Sections related to
email mostly now depend on [messages]/enabled now too. Set password via
link has been added to password resets.

lang.go

@@ -117,6 +117,7 @@ type setupLang struct {
 	JellyfinEmby       langSection `json:"jellyfinEmby"`
 	Ombi               langSection `json:"ombi"`
 	Email              langSection `json:"email"`
+	Messages           langSection `json:"messages"`
 	Notifications      langSection `json:"notifications"`
 	WelcomeEmails      langSection `json:"welcomeEmails"`
 	PasswordResets     langSection `json:"passwordResets"`