Add 404 page and improve form context functionality:

[d-rita]

What does this PR do?

• This PR adds a 404 page for non-existent routes. As well as pages still under development.
• It also improves the context functionality used on the Mapathon and UserGroup components.

Work done:

• Combine Mapathon and UserGroup context into one Form context provider.
• Use Form context with Mapathon and User Group components.
• Create a 404 card with a link to existing report pages.
• Create a Default Page component with map background.
• Use the Default Page component for both the Home and 404 pages.
• Redirect to the 404 page for undeclared routes.

How to test:

• Git pull and check out branch using git pull origin && git checkout feature/404-page
• Install dependencies using npm i
• Start the server using npm start
• Go to a random route, e.g /off

Screenshot:

Related issues:

• Fixes #82