MainLayout Component

[ryszard-put]

In Next.js it is recommended that there is Layout component which would be used for almost every page.
There is article about using _app.js custom component: https://reacttricks.com/nested-dynamic-layouts-in-next-apps.
It is also good opportunity to write global css rules.
As you explore our design, you will see that some components are repetitive, i.e. Navbar, Footer. We should put them into Layout Component.