nodejs scaffold generation for holochain-rust

This is a prototyping solution. Ideally this functionality would be built into the hc tool, potentially hc scaffold or integrated into hc init and hc generate.

Generates holochain hApp source code tree based off a single scaffold.json file, following these rules:

• Will not overwrite any source code in a file not prefixed with a "DO NOT MODIFY" comment
• Will generate stub files if not present
• Will generate "zome_def" from the scaffold, but functional code is placed in other modules

• Make sure the hc command is in your path. (in the holochain-rust directory, run make install_cmd).
• Make sure ./holochain-rust contains the holochain rust repo... can be a symlink

npm install
cd example
../bin/hcrs build