PLT-1527 Add a slash command to set yourself away (#3752)

* added handlers for slash commands

* added manual status persistance

* added tests

* removed extra debug output and comments

* rebase - fixing the PR

* making echo messages after slash commands ephemeral

model/status.go

@@ -18,6 +18,7 @@ const (
 type Status struct {
 	UserId         string `json:"user_id"`
 	Status         string `json:"status"`
+	Manual         bool   `json:"manual"`
 	LastActivityAt int64  `json:"last_activity_at"`
 }