Add Grid component

**Is your feature request related to a problem? Please describe.**
rimble doesn't offer a grid component that can hook up to the values in the theme.

**Describe the solution you'd like**
A Grid component with common styled-system props and access to the theme.

``
Default:
display: grid

Props:
gridGap
gridTemplateColumns
gridTemplateRows
gridTemplateAreas
...Box

``
Default:
grid-name: ${props => props.name}

Props:
...Box

**Describe alternatives you've considered**
using the native grid element

**Additional context**
https://styled-system.com/table#grid-layout

Acceptance criteria:
- Should have new Grid component
- Grid should have grid props
- Should have new GridArea component
- GridArea should have name props
- Grid and GridArea should extend Box

E: 1 D

Start by locating the existing Box component and related styled-system-based components in the repository, then compare their props and tests with the grid-layout reference linked in the issue. Add Grid and GridArea with the listed acceptance criteria, including theme-aware grid props and Box behavior, and verify the component tests cover the requested props and name handling.

Written by the indexing model from the issue text.