Specs for the gallery component

Changes

I'm looking into fixing potential bug with how attachments layout, but I wanted to start with adding some specs for the row function in the gallery component. When creating the specs I found some behavior that was weird to me, but it might be fine:

• Grouping of items is limited to a maxPerRow of 3 only for attachments at the end of the list
• If size: hide is set, no grouping happens and audio isn't set (I'm not sure what size: hide means, TBH)
• grid: true causes nothing to be grouped

I'm submitting this merge request to verify that this is the expected behavior before moving forward.

Thanks!