Component gallery UI updates

[trevor-e]

• adds spacing between each row for better visual grouping
• adds some small vertical margin on the checkerboard so that it's never flush with the view bounds
• adds a tap highlight color for each row
• centers the view preview for each row
• updates the checkerboard colors to match our web colors
• makes the view non-interactive for the list rows, but still interactive on the details page
• constrains the row width to the screen width so that some views don't overflow the screen

Normal:

Tapped row:

Details: