Fix order of input precedence

[vweevers]

The current order of input precedence for nom:npm is, with later overriding the former:

• defaults (hardcoded like license: "MIT" or external like npm and git config)
• configuration (like copyrightHolder, things that can't be derived from anything else)
• existing package.json
• cached answers
• answers
• options (from cli or parent generator)

It should be:

• defaults
• configuration and cached answers (handle as one, bypass Yeoman's cache)
• existing package.json
• answers
• options

[vweevers]

Putting a pin in this. @kessler we should discuss this sometime later. Because nom, bare-react and chrome-ninja all do roughly the same - like the above - without sharing code. Ideally I'd like to make a module that:

• Does strict option parsing (Yeoman does not coerce values, for example)
• Merges questions with options (specify an option to skip a question)
• Or somehow allows to specify questions and options in one go (same default value, validation)
• Has a long and short term memory (bare-react has this, so when used multiple times in a session - like chrome-ninja generating a popup app and option app - it will not ask twice whether you want ES6)

If done right, we could add additional features later (that every generator benefits from), like:

• A defaults or skipAll flag. If you just want to change one thing, you could do: yo x --skip-all --name new-name.