changes to content and adding infrastructure for demo tabs
changes to content and adding infrastructure for demo tabs

pair-code/what-if-tool,PAIR-code/what-if-tool,PAIR-code/what-if-tool,PAIR-code/what-if-tool,pair-code/what-if-tool,pair-code/what-if-tool,PAIR-code/what-if-tool,pair-code/what-if-tool,pair-code/what-if-tool,PAIR-code/what-if-tool