#1239: Establish how the React app will invoke the existing API

[ceciliazaragoza]

#1239

• can console.log() all of the demos.
• can access the local server from multiple hosts with an updated CORS configuration.
• added constants.js to hold constant values like the demo names.
• put the theme for Grommet styling in a separate theme.js.

[coveralls]

coverage: 80.06% (-0.3%) from 80.379%
when pulling 40272be on cecilia-1239
into ae4503b on beta.

[ceciliazaragoza]

To satisfy the coveralls requirements, I may need to add some tests to our current test suite because I am modifying code in web-client-classic.

[dondi]

LGTM—we will let the Coveralls callouts slide for now and look into ways to address them at a later time