Add vk bridge (#1372)

* Add vk bridge

* Vk bridge attachments

* Vk bridge forwarded messages

* Vk bridge sample config and code cleanup

* Vk bridge add vendor

* Vk bridge message edit

* Vk bridge: fix fetching names of other bots

* Vk bridge: code cleanup

* Vk bridge: fix shadows declaration

* Vk bridge: remove UseFileURL

vendor/github.com/SevereCloud/vksdk/v2/longpoll-bot/errors.go

@@ -0,0 +1,18 @@
+package longpoll
+
+import (
+	"fmt"
+)
+
+// Failed struct.
+type Failed struct {
+	Code int
+}
+
+// Error returns the message of a Failed.
+func (e Failed) Error() string {
+	return fmt.Sprintf(
+		"longpoll: failed code %d",
+		e.Code,
+	)
+}