Initial bot functionality

* The bot now properly joins the management room
* The management room is persisted in the database
* Welcome/help messages are sent in the management room

database/userquery.go

@@ -0,0 +1,27 @@
+package database
+
+import (
+	log "maunium.net/go/maulogger/v2"
+	"maunium.net/go/mautrix/id"
+)
+
+type UserQuery struct {
+	db  *Database
+	log log.Logger
+}
+
+func (uq *UserQuery) New() *User {
+	return &User{
+		db:  uq.db,
+		log: uq.log,
+	}
+}
+
+func (uq *UserQuery) GetByMXID(userID id.UserID) *User {
+	row := uq.db.QueryRow("SELECT mxid, id, management_room, token FROM user where mxid=$1", userID)
+	if row == nil {
+		return nil
+	}
+
+	return uq.New().Scan(row)
+}