Subtitle description and dimension update

[neovichsu]

Add subtitle, description and dimension update

• Adding subtitles and description onto px tile based on new px tile design
• Apply truncation on subtitle (single line) and description (can be specified by number of lines)
• Descriptions are now broken into two separate properties to allow use case in which the description text can be different from overlay description text.
• Apply new px tile layout design
• Add more px tile scss variables so developers can customize such as text color, multi-line truncation(ellipsis), height of description text, and height of overlay description text.
• New px tile color theme variables values will be added in px-theme as a separate PR.

Reviewers:
@mdwragg @randyaskin @katemenkhaus @german777

• working tests: WCT unit tests are added.

[mdwragg]

@Lizricharson53 ^^ of interest to you!