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/WorkflowEntity.ts

@@ -0,0 +1,55 @@
+import {
+	IConnections,
+	IDataObject,
+	INode,
+	IWorkflowSettings,
+} from 'n8n-workflow';
+
+import {
+	IWorkflowDb,
+} from '../../';
+
+import {
+	Column,
+	Entity,
+	PrimaryGeneratedColumn,
+} from 'typeorm';
+
+@Entity()
+export class WorkflowEntity implements IWorkflowDb {
+
+	@PrimaryGeneratedColumn()
+	id: number;
+
+	@Column({
+		length: 128
+	})
+	name: string;
+
+	@Column()
+	active: boolean;
+
+	@Column('json')
+	nodes: INode[];
+
+	@Column('json')
+	connections: IConnections;
+
+	@Column('timestamp')
+	createdAt: Date;
+
+	@Column('timestamp')
+	updatedAt: Date;
+
+	@Column({
+		type: 'json',
+		nullable: true,
+	})
+	settings?: IWorkflowSettings;
+
+	@Column({
+		type: 'json',
+		nullable: true,
+	})
+	staticData?: IDataObject;
+}