Refacor electron app and add migrations

electron/entities/AttachmentEntity.ts

@@ -0,0 +1,35 @@
+import {
+  Entity,
+  PrimaryColumn,
+  Column
+} from 'typeorm';
+
+@Entity('attachments')
+export class AttachmentEntity {
+  @PrimaryColumn('text')
+  id!: string;
+
+  @Column('text')
+  messageId!: string;
+
+  @Column('text')
+  filename!: string;
+
+  @Column('integer')
+  size!: number;
+
+  @Column('text')
+  mime!: string;
+
+  @Column('integer', { default: 0 })
+  isImage!: number;
+
+  @Column('text', { nullable: true })
+  uploaderPeerId!: string | null;
+
+  @Column('text', { nullable: true })
+  filePath!: string | null;
+
+  @Column('text', { nullable: true })
+  savedPath!: string | null;
+}