feat: Update navigation links on the website

[alainncls]

What does this PR do?

Updates links on the website landing page:

1. Outgoing links are marked with an icon
2. Adds links to the Explorer, the Documentation and our Twitter account

Navigation bar:

Footer:

Type of change

• Chore
• Bug fix
• New feature
• Documentation update

Check list

• Unit tests for any smart contract change
• Contracts and functions are documented

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (add2afa) 93.63% compared to head (8ba7641) 93.63%.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #526   +/-   ##
=======================================
  Coverage   93.63%   93.63%           
=======================================
  Files          20       20           
  Lines         330      330           
  Branches       76       76           
=======================================
  Hits          309      309           
  Misses         10       10           
  Partials       11       11           

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