Add BNS support when setting rewards address

[stjet]

Tested locally, working. This makes it more convenient for people with BNS (.ban) domains to login (no longer need to copy paste address from somewhere, which is especially inconvenient from other devices).

I tried to get it to work with the rollup thing, and make banani-bns a NPM dependency but couldn't get it working (sorry). Instead, added a script (bns.js) that sets the library on the window.bns property. The bns.js script is miniified, but can be reproduced by doing:

> git clone https://github.com/stjet/bns
> cd bns
> npm i
> npm run browser

Then checking the bns-browser.js file.

I wasn't sure what RPC to use, so it uses the kalium RPC for now, but can be changed easily.

Also edited the developer docs.

How to test

1. Go to /rewards/address
2. Type in a BNS domain, for example, nishina247.mictest.
3. Choose either option.
4. After a few seconds, the field will change to the Banano address resolved (in this case, ban_1o7ija3mdbmpzt8qfnck583tn99fiupgbyzxtbk5h4g6j57a7rawge6yzxqp), and the next step will use that address
   Success