More widget visual tweaks

[montehurd]

https://phabricator.wikimedia.org/T142762#2625348

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• Size of the Continue reading image should be the same as Top read articles' images. At the moment it is slightly bigger.
• Continue reading image should be in the same position as the Top read articles' images. Actual: It is slightly closer to the left (ie., greater padding on the RHS).
• Top read article images should be a square 86x86pt size. At the moment they are slightly narrower.
• Title of the expanded Top read widget (ie., where it says the Wikipedia language) should be in font type SF UI Display with the heavier font-weight Black (but still in the same color #555A5F)
  For some reason IB won't let me pick SF... can figure this out later
• Sparkline should move to always be below the last line of text rather than being locked in the bottom LHS corner of each list item.

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