Upgrade to Pattern Lab 3

[james-nash]

Closes #124

• Migrates to Pattern Lab 3.
• Removes BrowserSync tasks and dependency, as PL now has a built-in dev server

⚠️ Remember to run npm install when checking out this branch - the dependencies have changed!

Progress

• Migrated dependencies to new PL3 packages
• Updated PL Gulp tasks to use new PL
• Update any issues / incompatibilities in our Mustache files
• Investigate if we can (should?) still use BrowserSync or use PL3's built-in dev server
• Fix any outstanding bugs / quirks

[james-nash]

Our pattern library seems to build fine, but it outputs a load of warnings like this:

Could not replace height with 33 inside <svg role="img" class="{{styleModifier}}"{{#titleId}} aria-labelledby="{{titleId}}"{{/titleId}}{{#width}} width="{{width}}"{{/width}}{{#height}} height="{{height}}"{{/height}}>
  <use xlink:href="#buildit-logotype"></use>
</svg>

Most likely, they're related to us doing some funky pattern parameter stuff. Maybe it's no longer supported in PL3?

[danbull]

Minor comment, but the rest LGTM!

[danbull]

Just wondering what this does and why it's needed?

[james-nash]

Good spot!

I checked it out, according to the pattern lab docs, these are "live server"config options. It seems wait is an optional delay the server waits after changes, before reloading the browser(s).

I've tried removing the option and it seems to behave fine, so I'll commit that change now.