Fix some ESLint errors in cvat-core (#5537)

All of which are about old-style imports.

cvat-core/src/download.worker.js

@@ -2,7 +2,7 @@
 //
 // SPDX-License-Identifier: MIT
 
-const Axios = require('axios');
+import Axios from 'axios';
 
 Axios.defaults.withCredentials = true;
 Axios.defaults.xsrfHeaderName = 'X-CSRFTOKEN';

cvat-core/src/project-implementation.ts

@@ -5,11 +5,11 @@
 
 import { Storage } from './storage';
 
-const serverProxy = require('./server-proxy').default;
-const { getPreview } = require('./frames');
+import serverProxy from './server-proxy';
+import { getPreview } from './frames';
 
-const Project = require('./project').default;
-const { exportDataset, importDataset } = require('./annotations');
+import Project from './project';
+import { exportDataset, importDataset } from './annotations';
 
 export default function implementProject(projectClass) {
     projectClass.prototype.save.implementation = async function () {

cvat-core/src/project.ts

@@ -6,11 +6,11 @@
 import { StorageLocation } from './enums';
 import { Storage } from './storage';
 
-const PluginRegistry = require('./plugins').default;
-const { ArgumentError } = require('./exceptions');
-const { Label } = require('./labels');
-const User = require('./user').default;
-const { FieldUpdateTrigger } = require('./common');
+import PluginRegistry from './plugins';
+import { ArgumentError } from './exceptions';
+import { Label } from './labels';
+import User from './user';
+import { FieldUpdateTrigger } from './common';
 
 /**
  * Class representing a project