Make component unit test for component/panel/color.js

[hideokamoto]

Description

Related to progress on the issue -> Unit Testing Components #641

Added some unit test scripts for PanelColor component.

How Has This Been Tested?

Run unit test command.

$ npm test
 PASS  components/panel/test/color.js
  PanelColor
    ✓ should match snapshot (19ms)
    ✓ should match snapshot when title is empty (3ms)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows has proper inline documentation.

[gziolo]

I feel like one snapshot test would be enough here. The second test could only validate if the title is set properly. Let's merge as it is. I will open a follow up to explain what I mean :) Thanks for adding those tests 👍