Update template documentation to include DataList methods

https://github.com/silverstripe/sapphire/pull/1799.
FIX JSONDataFormatter wrong relation identifiers (fixes #1795)
Consistently used dollar notation in template docs (see #1794)
FIX Only block root vendor folder

Use RewriteRule instead to take in account any subfolder via RewriteBase. Deny ss-cache and composer via RewriteRule too.