Feature: enable dependencies for use in `denim.js`

[ryan-roemer]

Presently we advise against using any dependencies in a denim.js file, mostly because of the chicken-and-egg problem of not knowing what's available.

However, we require this in denim itself and could expose functionality to:

• [ ] install <module>/package.json dependencies
• [ ] which would make things requireable
• [ ] Possible enable this setting as a flag to "install the templates module dependencies"

... or some other approach. The above works great for standalone template modules that have no other deps, but would be awkward for things like builder archetypes that have dependencies as part of the archetype.