Normalize naming conventions
The goal of this issue is to normalize naming conventions throughout the codebase. This means changing the `cabin.json` spec and cli inputs to have a consistent name for a piece of information throughout the site creation process.
## cabin.json property renaming

template -> templateEngine
style - > preprocessor
## config.js added property naming

preprocessorGruntTask -> used when rendering the _package.json and _Gruntfile.js
templateFileExtension -> used when rendering the cabin.json
