Add margin options of images and grid padding for 2 col layout

[nsolerieu]

Issues:

• Images added to page markdown content automatically get a margin bottom applied
• Grid automatically get lateral padding creating an indentation that break the vertical flow

Example:

Suggested fixes:

• Default to no margin for image nested in a grid (to not affect all other images
• Offer margin/padding utility classes for Grid .no-padding .no-margin via the React components

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