Include local blocks for hub assistants

[RomneyDa]

Description

Adds support for local blocks to hub assistants Achieves this by creating a simple "dud" assistant to unroll, made up of any local blocks Moves some utils around, including retrieval of local block files and creation of a registry. This is mostly so that adding this support for JSON is simple in the future.

This should be followed by a PR to add support for JSON