Move dictionary to dedicated page

Description

This PR contains work for moving the dictionary to a dedicated page. As a by-product of that, content has moved from the home page to more dedicated pages as well, and a basic navigation has been added.

Motivation and Context

The goal is to open up the home page to speak more about the project and highlight important information about the project and supporting it.

How Has This Been Tested?

So far only locally on my machine and brief QA with @tatianamac

Screenshots (if appropriate):

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

[x] I have read the CONTRIBUTING document.
[x] My code follows the code style of this project.
[ ] I have added tests to cover my changes.
[ ] All new and existing tests passed.

selfdefined / web-app

Move dictionary to dedicated page #458