Switch to storing To addresses as a slice

- Changes on-disk storage format
- Changes JSON API
- To and From values are now parsed/formatted by Go's mail.ParseAddress
  function
- Fixed bug in list-entry-template, was not escaping HTML characters
- Updated tests

rest/apiv1_controller_test.go

@@ -95,7 +95,7 @@ func TestRestMailboxList(t *testing.T) {
 		Mailbox: "good",
 		ID:      "0001",
 		From:    "from1",
-		To:      "to1",
+		To:      []string{"to1"},
 		Subject: "subject 1",
 		Date:    time.Date(2012, 2, 1, 10, 11, 12, 253, time.FixedZone("PST", -800)),
 	}
@@ -103,7 +103,7 @@ func TestRestMailboxList(t *testing.T) {
 		Mailbox: "good",
 		ID:      "0002",
 		From:    "from2",
-		To:      "to1",
+		To:      []string{"to1"},
 		Subject: "subject 2",
 		Date:    time.Date(2012, 7, 1, 10, 11, 12, 253, time.FixedZone("PDT", -700)),
 	}