Support for SLP partial agora offers (listing fungible SLP tokens)
This diff is large. I think I have split out everything that can be split out.
**Reviewer notes**
For practical purposes, it's best to review this diff in some component parts. It's not practical to stack the diff into these parts, as these things need to happen at the same time (i.e. a user needs to be able to list, buy, and cancel an offer as soon as we launch support for this feature).
[] Addition of a new screen, Agora, and its navigation / icon (see `assets/doge.svg`, `components/App/App.js`, `App.test.js`, `components/Common/CustomIcons.js`)
[] Changes to the Token screen, where users can now create Agora offers to sell their tokens (see `components/Etokens/Token/index.js` and tests)
[] Associated validation functions for agora partial offer creation in `validation/index.js` and tests
[] The Agora screen, where users can see active offers and cancel their own offers (see `components/Agora/index.js`, `components/Agora/OrderBook.js`, and tests in same dir
[] new formatting functions in formatting.js