Refacor electron app and add migrations

electron/entities/MetaEntity.ts

@@ -0,0 +1,10 @@
+import { Entity, PrimaryColumn, Column } from 'typeorm';
+
+@Entity('meta')
+export class MetaEntity {
+  @PrimaryColumn('text')
+  key!: string;
+
+  @Column('text', { nullable: true })
+  value!: string | null;
+}