Jetpack Plugins: all sites single plugin management tables could use a padding/margin scrub

[v18]

Reported by @rickybanister: Currently the table looks like this on the single site plugin page at https://wordpress.com/plugins/akismet :

There are a couple of issues:

• Tight padding around the sub sites
• Left and right padding is non-standard
• Border between sub sites is too dark, it should match the folding card's header border color

Here's a quick screengrab after messing with the inspector (ignore typography changes and stuff):