Reorganize project. Add folder for shared code between backend/dashboard. Switch from jest to ava for tests.

backend/src/data/entities/UsernameHistoryEntry.ts

@@ -0,0 +1,14 @@
+import { Entity, Column, PrimaryColumn } from "typeorm";
+
+@Entity("username_history")
+export class UsernameHistoryEntry {
+  @Column()
+  @PrimaryColumn()
+  id: string;
+
+  @Column() user_id: string;
+
+  @Column() username: string;
+
+  @Column() timestamp: string;
+}