Website: add banner image to be used in the README.

Progress on #216.
Improve README with a banner, download links, and improved wording.

- Add a banner image to the top of the file
- Use SVG badges
- Improve the description of the framework
- Add a Download section with links to release files and npm/Bower
- Streamline the Overview and Benefits sections
- Bring the Get Started and Get Help sections in line with the website
- Remove the Response Processing section in favor of the website version

Closes #216.
Merge pull request #215 from nicksay/spiffy-readme

Website: add banner image to be used in the README.
Merge pull request #217 from nicksay/spiffy-readme-2

Improve README with a banner, download links, and improved wording.
Fix typo in website link in the README file.
Merge pull request #219 from nicksay/spiffy-readme-typo

Fix typo in website link in the README file.
Merge pull request #214 from nicksay/server-utils-python

Refactor reusable parts of the demo app into standalone Python module.
Convert Python code to comply with PEP 8 style guide.