implement the imap metadata extension, rfc 5464

this allows setting per-mailbox and per-server annotations (metadata). we have
a fixed maximum for total number of annotations (1000) and their total size
(1000000 bytes). this size isn't held against the regular quota for simplicity.
we send unsolicited metadata responses when a connection is in the idle
command and a change to a metadata item is made.

we currently only implement the /private/ namespace.  we should implement the
/shared/ namespace, for mox-global metadata annotations.  only the admin should
be able to configure those, probably through the config file, cli, or admin web
interface.

for issue #290

webmail/api.go

@@ -1230,7 +1230,7 @@ func (Webmail) MailboxCreate(ctx context.Context, name string) {
 	})
 }
 
-// MailboxDelete deletes a mailbox and all its messages.
+// MailboxDelete deletes a mailbox and all its messages and annotations.
 func (Webmail) MailboxDelete(ctx context.Context, mailboxID int64) {
 	reqInfo := ctx.Value(requestInfoCtxKey).(requestInfo)
 	acc := reqInfo.Account

webmail/api.json

@@ -276,7 +276,7 @@
 		},
 		{
 			"Name": "MailboxDelete",
-			"Docs": "MailboxDelete deletes a mailbox and all its messages.",
+			"Docs": "MailboxDelete deletes a mailbox and all its messages and annotations.",
 			"Params": [
 				{
 					"Name": "mailboxID",

webmail/api.ts

@@ -894,7 +894,7 @@ export class Client {
 		return await _sherpaCall(this.baseURL, this.authState, { ...this.options }, paramTypes, returnTypes, fn, params) as void
 	}
 
-	// MailboxDelete deletes a mailbox and all its messages.
+	// MailboxDelete deletes a mailbox and all its messages and annotations.
 	async MailboxDelete(mailboxID: number): Promise<void> {
 		const fn: string = "MailboxDelete"
 		const paramTypes: string[][] = [["int64"]]

webmail/msg.js

@@ -573,7 +573,7 @@ var api;
 			const params = [name];
 			return await _sherpaCall(this.baseURL, this.authState, { ...this.options }, paramTypes, returnTypes, fn, params);
 		}
-		// MailboxDelete deletes a mailbox and all its messages.
+		// MailboxDelete deletes a mailbox and all its messages and annotations.
 		async MailboxDelete(mailboxID) {
 			const fn = "MailboxDelete";
 			const paramTypes = [["int64"]];

webmail/text.js

@@ -573,7 +573,7 @@ var api;
 			const params = [name];
 			return await _sherpaCall(this.baseURL, this.authState, { ...this.options }, paramTypes, returnTypes, fn, params);
 		}
-		// MailboxDelete deletes a mailbox and all its messages.
+		// MailboxDelete deletes a mailbox and all its messages and annotations.
 		async MailboxDelete(mailboxID) {
 			const fn = "MailboxDelete";
 			const paramTypes = [["int64"]];

webmail/webmail.js

@@ -573,7 +573,7 @@ var api;
 			const params = [name];
 			return await _sherpaCall(this.baseURL, this.authState, { ...this.options }, paramTypes, returnTypes, fn, params);
 		}
-		// MailboxDelete deletes a mailbox and all its messages.
+		// MailboxDelete deletes a mailbox and all its messages and annotations.
 		async MailboxDelete(mailboxID) {
 			const fn = "MailboxDelete";
 			const paramTypes = [["int64"]];