Andrew/card component

[andrewhatran]

Add spectrum card component and some of its variations.

Description

Add spectrum card, gallery card, and quiet card. Add a demo page showcasing each component

Motivation and Context

Decided to start with a simple component as a POC. The card component was a good choice since it takes in dynamic content but was relatively simple.

How Has This Been Tested?

Testing of the component variations was done through the the card demo page.

Screenshots (if appropriate):

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• [x ] I have signed the Adobe Open Source CLA.
• [x ] My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[benjamind]

Looks like an excellent first implementation. Couple of minor comments. I think we should move subtitle text into an attribute since it probably shouldn't be rich content and is more inline with title text then, other than that looks good. Though we do need to setup dynamic rendering for changing of attributes since we don't get that without the use of lit-element, but thats a task for another day.