webadmin: be more helpful when adding domains/accounts/addresses

by explaining (in the titles/hovers) what the concepts and requirements are, by
using selects/dropdowns or datalist suggestions where we have a known list, by
automatically suggesting a good account name, and putting the input fields in a
more sensible order.

based on issue #132 by ally9335

config/config.go

@@ -107,7 +107,7 @@ type SpecialUseMailboxes struct {
 // Dynamic is the parsed form of domains.conf, and is automatically reloaded when changed.
 type Dynamic struct {
 	Domains            map[string]Domain  `sconf-doc:"NOTE: This config file is in 'sconf' format. Indent with tabs. Comments must be on their own line, they don't end a line. Do not escape or quote strings. Details: https://pkg.go.dev/github.com/mjl-/sconf.\n\n\nDomains for which email is accepted. For internationalized domains, use their IDNA names in UTF-8."`
-	Accounts           map[string]Account `sconf-doc:"Accounts to which email can be delivered. An account can accept email for multiple domains, for multiple localparts, and deliver to multiple mailboxes."`
+	Accounts           map[string]Account `sconf-doc:"Account represent mox users, each with a password and one or more email addresses to which email can be delivered (possibly different domains). Each account has its own on-disk directory holding its messages and index database. An account name has is not an email address."`
 	WebDomainRedirects map[string]string  `sconf:"optional" sconf-doc:"Redirect all requests from domain (key) to domain (value). Always redirects to HTTPS. For plain HTTP redirects, use a WebHandler with a WebRedirect."`
 	WebHandlers        []WebHandler       `sconf:"optional" sconf-doc:"Handle webserver requests by serving static files, redirecting or reverse-proxying HTTP(s). The first matching WebHandler will handle the request. Built-in handlers, e.g. for account, admin, autoconfig and mta-sts always run first. If no handler matches, the response status code is file not found (404). If functionality you need is missng, simply forward the requests to an application that can provide the needed functionality."`
 	Routes             []Route            `sconf:"optional" sconf-doc:"Routes for delivering outgoing messages through the queue. Each delivery attempt evaluates account routes, domain routes and finally these global routes. The transport of the first matching route is used in the delivery attempt. If no routes match, which is the default with no configured routes, messages are delivered directly from the queue."`