Infer contract name from metadata

[wottpal]

It would be awesome if when I "Add contract from address", it would infer the actual contract name from the json contents. Currently, it just names them all "New Contract".

When inferring the name (as stated above), it would be better to take the name from the contract.name field instead of inferring the filename. Because we are currently still using metadata.json for all abi's (like it was before) and keep them in differently named folders instead.

cc @statictype