Adding Sam.gov implementations.

Sam-Styles - https://github.com/GSA/sam-styles - HTML/CSS design library built on USWDS 2.0 and Fractal.
Sam-Design-System - https://github.com/GSA/sam-design-system - Common Angular components integrated with sam-styles css framework.
Sam-Prototypes - https://github.com/GSA/sam-prototypes - A test application that incorporates sam-styles and sam-design-system components with real-world examples.

UI components: For pull requests that impact the look, feel, or functionality of USWDS itself, please open a pull request on the web-design-standards repo (https://github.com/uswds/uswds-site).

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Description

Include a high-level description of the issue your pull request fixes; include only one issue per pull request. Please also link to the GitHub issue it resolves.

Additional information

Include any of the following (as necessary):

• Relevant research and support documents
• Type of content review needed: stylistic or copy editing
• Screenshot images
• Notes
• etc.

Before you hit Submit, make sure you’ve done whichever of these applies to you:

• Follow the 18F Front End Coding Style Guide and Accessibility Guide.
• Run npm test and make sure the tests for the files you have changed have passed.
• Run your code through HTML_CodeSniffer and make sure it’s error free.
• Title your pull request using this format: [Website] - [UI component]: Brief statement describing what this pull request solves.