[DShop] Display token images for ERC-20 tokens during checkout

Original issue: https://github.com/OriginProtocol/dshop/issues/320

Summary: DShop allows merchants to accept custom ERC-20 tokens as payment. However, when a DShop customer reaches the 'Checkout' page, they may not see icons corresponding to the ERC-20 tokens configured for payment. Despite there being little resistance to the idea of displaying token images, there is no clarity on where we might get these token images from.

Specifically speaking, a solution to the above-mentioned issue was offered via https://github.com/OriginProtocol/dshop/pull/852. As noted, I authored code to fetch token images from one of two sources:

1. TrustWallet's Github repository
2. Ethereum Lists

Although a community member was concerned that sourcing images from a Github repository is introducing a "dependency", I stand by what I said in the thread -- having A solution is better than having NONE. Moreover, our reliance on a centralized resource like TrustWallet is alleviated by having Ethereum Lists (a decentralized alternative) as a 'fallback'. With us having the ability to display images for over 6000 unique tokens right now, I question whether we really need to keep waiting for a 'better' solution to come along.

Please vote to show support for merging the authored code into DShop's codebase.