FEAT: Add mobile menu using javascript for the event management.

[joramot]

Features:

• When the user clicks the hamburger button, the mobile menu appears.
• When the user clicks the close (X) button, the mobile menu disappears.
• When the user clicks any of the mobile menu options, the mobile menu disappears.
• When the user clicks any of the mobile menu options, a correct part of the page is displayed.
• Add structure with one 'div' tag in the index.html to define the nav menu for the mobile version.
• Add CSS classes to give styles to the nav menu for the mobile version.
• Create the menu.js file to define the instructions for the events management