Add common grid patterns

[andesol]

Done

• Add three new classes that could work as alias for common grid patterns (.row--50-50, .row--25-75, .row--25-25-50)

Fixes WD-2886

QA

• Open the example
• Resize the screen and check it behaves according to the docs

Check if PR is ready for release

If this PR contains Vanilla SCSS code changes, it should contain the following changes to make sure it's ready for the release:

• PR should have one of the following labels to automatically categorise it in release notes:
  • Feature 🎁, Breaking Change 💣, Bug 🐛, Documentation 📝, Maintenance 🔨.
• Vanilla version in package.json should be updated relative to the most recent release, following semver convention:
  • if CSS class names are not changed it can be bugfix relesase (x.x.X)
  • if CSS class names are changed/added/removed it should be minor version (x.X.0)
  • see the wiki for more details
• Any changes to component class names (new patterns, variants, removed or added features) should be listed on the what's new page.

[webteam-app]

Demo starting at https://vanilla-framework-4727.demos.haus

[anthonydillon]

This is good but it's highly likely that we are going to want to link directly to a layout pattern. For example, in a review the designer might say we should use the 25-25-50 pattern here with a link. So individual examples and headed docs would be useful.

[andesol]

@bartaz Ready!

[bartaz]

LGTM, thanks!