Convert remaining roomserver tables (#1065)

* Convert invites table

* Convert membership table

* Factor out remaining functions except for *Updater structs

* Remove 'implements' comments from long-forgotten interfaces. Move those comments to storage.Database

roomserver/storage/shared/prepare.go

@@ -0,0 +1,36 @@
+// Copyright 2017-2018 New Vector Ltd
+// Copyright 2019-2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package shared
+
+import (
+	"database/sql"
+)
+
+// StatementList is a list of SQL statements to prepare and a pointer to where to store the resulting prepared statement.
+type StatementList []struct {
+	Statement **sql.Stmt
+	SQL       string
+}
+
+// Prepare the SQL for each statement in the list and assign the result to the prepared statement.
+func (s StatementList) Prepare(db *sql.DB) (err error) {
+	for _, statement := range s {
+		if *statement.Statement, err = db.Prepare(statement.SQL); err != nil {
+			return
+		}
+	}
+	return
+}