Added support for MySQL

* In packages/cli/src/Db.ts, conditional test of dbType replaced by a
switch;
* removeAll() function adapted to not cause an error using MySQL;
* Added the cross-env module in the "serve" script in the
packages/editor-ui/package.json file. This was done to ensure
compatibility between platforms when declaring environment variables.
Without it, Windows compilation would give an error, for example;
* .idea added to .gitignore (IntelliJ IDEA solutions);

packages/cli/src/databases/mysqldb/CredentialsEntity.ts

@@ -0,0 +1,44 @@
+import {
+	ICredentialNodeAccess,
+} from 'n8n-workflow';
+
+import {
+	ICredentialsDb,
+} from '../../';
+
+import {
+	Column,
+	Entity,
+	Index,
+	PrimaryGeneratedColumn,
+} from 'typeorm';
+
+@Entity()
+export class CredentialsEntity implements ICredentialsDb {
+
+	@PrimaryGeneratedColumn()
+	id: number;
+
+	@Column({
+		length: 128
+	})
+	name: string;
+
+	@Column('text')
+	data: string;
+
+	@Index()
+	@Column({
+		length: 32
+	})
+	type: string;
+
+	@Column('json')
+	nodesAccess: ICredentialNodeAccess[];
+
+	@Column('timestamp')
+	createdAt: Date;
+
+	@Column('timestamp')
+	updatedAt: Date;
+}