Merge pull request #276 from jay-hodgson/shiny-whitelist

include shiny.synapse.org in whitelist
Merge pull request #275 from jay-hodgson/SWC-489-round2

SWC-489: pull heading inner html to style ToC items
SWC-523: move shiny to alpha and SWC-452: target markdown tables
Merge alpha shiny widget and markdown table css targetting into release-1.24