Create a custom card grid component for rich text editors

[kevinsmaster5]

Closes #237

Changes proposed in this pull request:

• Adds CardGrid as a BlocksFeature to allow users to create a card grid component
  • user can select number of columns 1 - 6
  • cards have optional image, title, and description fields
  • cards may be set up as vertical or horizontal - "flag" orientation (left or right image placement)

pages-site-gantry implementation notes

CardGrid slug: 'cardGrid'

Block node schema

 {
   id:
   image: {
     id:
     altText:
     ...
     url:
     filename:
   title:
   description:
   orientation: ( vertical, horizontal, horizontal-right )
 }

Things to check

• For any logging statements, is there any chance that they could be logging sensitive data?
• Are log statements using a logging library with a logging level set? Setting a logging level means that log statements "below" that level will not be written to the output. For example, if the logging level is set to INFO and debugging statements are written with log.debug or similar, then they won't be written to the otput, which can prevent unintentional leaks of sensitive data.

Security considerations

This change adds a CardGrid FeatureBlock and doesn't create security exposure

[apburnes]

Let's grid it