Add flow to api/server/server.js
Add flow check to src/api: index, accountinfo, balances, orderbook..
orders, settings, transaction, transactions
Add flow typecheck to api/ledger/pathfind
Use eslint plugin flowtype to allow flow type annotations
Babel-eslint emits errors when using the type keyword. This plugin works
around the issue by stripping flow annotations before linting.
Source: https://www.npmjs.com/package/eslint-plugin-flowtype
Add flow to ledger/parse/account-order, trustline, orderbook-order