Warn of payments to exchanges without memo

[ghost]

We see so many users forgetting to set the memo when sending funds to exchanges like Bittrex and Kraken that we should consider displaying a warning when they try to do so. I've noticed stellarchain, stellar dashboard, and stellar expert all identify these exchanges (perhaps by home domain? or is this hard coded?).

[ghost]

I see dashboard has a known_accounts.js. Is this something that is useful to maintain separately and host on a CDN? As more projects need to keep a registry of accounts it's maybe a good idea to have only a single source to keep up to date.

[bartekn]

Yes, we will extract known_accounts.js and maybe create a web service around it. I think that PR adding this feature (with static list of exchanges in the beginning) will be approved.