Re-align dash.ttl and dash.js between shacl and shacl-js repos

[HolgerKnublauch]

There is currently a misalignment between the versions of dash.ttl and dash.js (and related files) between this shacl-js repo and the sibling shacl repo (for the public Java API). Yet another version lives in the private TopQuadrant repo from which the next product releases are built.

All these should be using the same code, where possible. In particular though, the dash.ttl should have the same content and offer the same features, because that namespace is supposed to be stable and reliable.