GOV.UK Frontend release v0.0.26-alpha

0.0.26-alpha (Breaking release)

Breaking changes:

• The error summary component now has a default bottom margin
  (PR #583)
• Nest components correctly
  (PR #584)

Fixes:

• Make section break line 1px instead of 2px
  (PR #585)

New features:

• Add footer component (PR #569)

Internal:

• Update pre-release step to check for new components
  (PR #574)
• Ensure render function does not have undefined object
  (PR #587)
• Fix components relying on global builds
  (PR #588)