Feature/628 starterkit config

[tburny]

Addresses #628 StarterKits should be able to override settings in patternlab-config.json

Summary of changes:

1. read starterkit-config.json
2. Deep merge into patternlab-config.json. Existing object keys are overwritten, including array values.
3. Save result to patternlab-config.json

[bmuenzenmeyer]

I fear I may have misdirected your work on this one @tburny

You can see here how this value is used on the frontend: https://github.com/pattern-lab/styleguidekit-assets-default/search?utf8=%E2%9C%93&q=patternExtension

To me, it makes a lot more sense to have the patternengine potentially set this value, if anything. In a user's workflow, it feels like the engine provided more utility over the starterkit in dictating a change to this value, if anything (it's likely a one-time edit).

Are there other keys that you can envision a starterkit needing to overwrite/merge upon installation?

[tburny]

Are there other keys that you can envision a starterkit needing to overwrite/merge upon installation?

Just to be clear what the vision is: A 10 seconds PL setup. As a user, I first choose a plain PL or Gulp/Grunt edition (Side note: The default PL config differs between the two!). Then I'll choose a starter kit and load it.
Each starter kit could come in different flavours:

• Different template engine (template extension)
• Different source paths (e.g. javascript instead of js, img instead of images, etc.)
• Different pattern group naming ( e.g. dna, cell, organism) resulting in other names for styleguideExcludes
• Using LESS instead of SASS: ignored-directories: ["less"]

I think the StarterKit should have the flexibility to meet a user's desires, that is to ship with the configuration required to run it :) Also, if you have 3 pattern engines installed, with mustache being already installed as part of PL, how would you determine the patternExtension required for a certain StarterKit?