Blockscout: Design cleanup for contract page and read/verify contract

[acravenho]

The following pages need some design cleanup:

• [x] contract page
• [x] read smart contract page
• [x] verify smart contract page

[jimmay5469]

I am removing mockup for ERC-721 support (#463) from the list above as we can just track the mockup work for that on #463 itself.

[jimmay5469]

I am removing Include a Token details page (#486) @katibest @arthurra Please ping me when you start work here. I would like to discuss adding 1 more type field (ERC20 or ERC721) from the list above. I created #524 to track this work.

[jimmay5469]

I am removing Adds API docs page with 'try it' UI #499 from the list above. I created #525 to track this work.

[jimmay5469]

I am renaming this issue to only deal with the 3 contract checklist items left in the list above.