Add landing page that shows the current configurations of Antennas

[jfarseneau]

Notable Changes

• Adds a landing page showing the current configuration of your Antennas proxy.
• README has been updated with logo and screenshot of the landing page, as well as better instructions to build Antennas.
• A new endpoint has been added, /antennas_config.json that returns the Antennas configurations.
• A 404 page was added, replacing Kemal's default.
• Antennas is now set up for easier dev, as it has a watcher that autorefreshes when there's a change to the public folder. This might be a problem for production environments however, and could be refined to only be added in a dev environment.