Scaffolder: Allow for more complex features to be generated

[srtfisher]

Description

I would like to be able to replicate the functionality of the (internal to Alley) site scaffolder. For example, more complex functionality such as generating a fields, post types, taxonomies, etc. that aren't straight compile and write generations. These generations will require modifications/insertions into files.

This will be possible through custom features written in Javascript (not just YAML).

Use Case

When a user uses the scaffolder they should be able to generate complex features such as post types, taxonomies, and fields.