New gutter system

The current gutter system is awkward and depends on `.frow-container` in some situations to avoid the negative margins from colliding with other page margins. `.frow-container` should be removed the equation completely.

Perhaps a new set-up would be something like:
```

```

The negative margins would be applied directly to `.gutters`. Is this better? Does it solve the problem?

Start by reviewing the current `.frow-container` and negative-margin behavior, then compare it with the proposed `.gutters` wrapper around `.frow`. Determine whether moving the negative margins to `.gutters` removes the dependency and prevents collisions with page margins. Done means the new arrangement is specified clearly and its effect is validated against the reported layout problem.

Written by the indexing model from the issue text.