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/statistics.model.ts

@@ -0,0 +1,11 @@
+export interface IStatistics {
+  numberOfUsers: number;
+  numberOfEvents: number;
+  numberOfLocalEvents: number;
+  numberOfComments: number;
+  numberOfLocalComments: number;
+  numberOfGroups: number;
+  numberOfLocalGroups: number;
+  numberOfInstanceFollowings: number;
+  numberOfInstanceFollowers: number;
+}