Feature/next/fractal

[c1rrus]

Closes #264
Related to #106

Description
Ditches Pattern Lab and migrates to Fractal as our tool for generating the pattern library website.

While Pattern Lab has served us well over the years, there are additional features that Fractal has which are useful to us:

• Ability to use different preview layouts per component. E.g.: We could use this to have a preview that overrides the usual flex on body stuff for individual components, and another which does not for templates and pages
• Grouping component files into folders. It's nice to have the data, docs and template altogether as a unit. This also makes it easier if we want to reorder or reorganise components, since we only need to change the directory name
• We can use Fractals API to make a customised component template export function (they have an example and I have done something very similar in a personal project, so can confirm it works). This will help pave the way to publishing the Nunjucks templates as an NPM package for other projects to consume
• Ability to use JS files to provide context data. We could use this to auto-generate dummy content or fetch realistic content from some APIs. Saves writing everything out as JSON manually!

Notes for reviewers
The vast majority of changes are simple file renames. Where individual patterns in Pattern Lab were like this:

some/
    category/
        12-pattern-name.njk   # template
        12-pattern-name.md    # description text
        12-pattern-name.json  # context data

The equivalent files in Fractal are like this:

some/
    category/
        12-pattern-name/
            pattern-name.njk          # template
            README.md                 # description text
            pattern-name.config.json  # context data

Additionally, the JSON files need a top-level context property, whose value is the context data. This is because these files can contain other kinds of per-pattern configuration info too.

The more interesting changes are in the Gulp scripts. All Pattern Lab stuff has been removed and replaced with the equivalent Fractal functionality. Feel free to ping me if you want me to talk you through any of it.

[ashblue]

Minor adjustments. Please be sure to include a linter rule for whitespace.

[ashblue]

Leftover comment block, delete or restore please.

[c1rrus]

Good spot. It's been restored now.

[ashblue]

Please include a lint check for concurrent whitespace.

[c1rrus]

I've just rebased on the current next branch, which contains your recent, shared ESLint setup. I've fixed all the stuff that was being flagged - including the double blank lines - and it's oh so pretty now! ^_^

[danbull]

Looks good to me! I think this is probably an example of a feature that may have to be manually merged in? #329

[james-nash]

I think this is probably an example of a feature that may have to be manually merged in? #329

Not sure what you mean? I just had a look and don't think anything related to #329 got lost in this transition.

[danbull]

I think this is probably an example of a feature that may have to be manually merged in? #329

Not sure what you mean? I just had a look and don't think anything related to #329 got lost in this transition.

Apologies, long story but ignore me, can confirm it's all good.

[james-nash]

FYI: This did get merged. Github somehow got a bit confused though, so I had to "close" this PR afterwards.