build: switch from yarn to npm to manage js dependencies and move js contents to root

yarn v1 is being deprecated and starts to have some issues

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

src/types/stats.model.ts

@@ -0,0 +1,5 @@
+export interface CategoryStatsModel {
+  key: string;
+  number: number;
+  label?: string;
+}