Einstein Analytics: A robust approach for performing period over period analysis (using a single date picker)

Einstein Analytics dashboard pattern for dynamic Period over Period Analysis using a single date picker. Highlights: * Works with a single standard date widget * Works with absolute dates * Works with relative date bonus Allows switching between \"current period vs. prior period\" (example: Jan-Feb 2019 vs. Nov-Dec 2018) & \"current period vs same period prior year\" (example: Jan-Feb 2019 vs. Jan-Feb 2018)