switch to mongodb, add drag&drop

backend/src/models/mod.rs

@@ -0,0 +1 @@
+pub mod user_model;

backend/src/models/user_model.rs

@@ -0,0 +1,11 @@
+use mongodb::bson::oid::ObjectId;
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct User {
+    #[serde(rename = "_id", skip_serializing_if = "Option::is_none")]
+    pub id: Option<ObjectId>,
+    pub username: String,
+    pub email: String,
+    pub password: String,
+}