Use fenced code blocks in promotions and activators guides
Add promotions to sidebar
Add link to activators
Revert "Fixed link - also using markdown instead of link to"

This reverts commit 3ec4f57b5687a0cb5b5fcb744486540c98a0b1cb.
Add the checkout flow customization guide
Add addresses and taxation to sidebar
Fix code examples in activators and promotions guides
Fix link to preferences in checkout guide
Fix usage of shell in place of bash in navigating+about guides
Convert preferences guide to new format