Improved: Add new custom block "DetailsBlock" with expanding answers and demonstrate it in a BreadPage and in a new FAQ page

[gzark1]

This PR is an improvement of #422. I deleted the DetailsBlock option from BaseStreamBlock, in order not to complicate things. I utilized DetailsStreamBlock in both BreadPage (and demonstrated it in "Anadama" bread) and StandardPage (demonstrated it in "FAQ"). I stored the data i created in bakerydemo/base/fixtures/bakerydemo.json, keeping only the necessary changes.