BHV-6058: Add flex box implementation of Fittables, to avoid intermediat...

...e JS re-layouts on supported platforms.  Update samples to avoid use of percentage-sized children (which is a rare use case and not supported by flex box); instead, use media queries to ensure the samples look reasonable on different sized-screens (which fits more closely to best practices).

DCO-1.1-Signed-Off-By: Kevin Schaaf <kevin.schaaf@lge.com>