Add managesieve (Sieve) support for remote accounts

When switching identities, the managesieve plugin still connected to
the default sieve server. Hook into managesieve_connect to redirect
the sieve connection to the remote account's server.

Adds sieve_host, sieve_port and sieve_auth columns to the database,
a Sieve section to the identity settings form, preconfig support for
sieve_host, and localized labels for all 7 languages.

SQL/mysql.initial.sql

@@ -37,6 +37,15 @@ CREATE TABLE IF NOT EXISTS `ident_switch`
 		smallint
 		NOT NULL
 		DEFAULT 1,
+	`sieve_host`
+		varchar(64),
+	`sieve_port`
+		int
+		CHECK(`sieve_port` > 0 AND `sieve_port` <= 65535),
+	`sieve_auth`
+		smallint
+		NOT NULL
+		DEFAULT 1,
 	`drafts_mbox`
 		varchar(64),
 	`sent_mbox`