Merge pull request #19 from Elfoslav/dependabot/npm_and_yarn/tar-4.4.15

Merge pull request #17 from Elfoslav/dependabot/npm_and_yarn/lodash-4.17.21

Bump tar from 4.4.13 to 4.4.15

Bump lodash from 4.17.20 to 4.17.21

Fix MAIL_URL of undefined

Update readme

Update Meteor & Packages

Fixed error message in Integer variables Exercise 1

Added video in theory for the first 15 JS lessons

Fixed a grammar mistake in Hello world lesson

Sort notifications by timestamp in ASC order

Checking for indentation in conditions exercise 1 and 2

Showing CSS, JS, HTML and Meteor.js study groups on homepage

Sort study groups by userIds

Fixed creating study group if there is no curriculum