Better rate-limit error handling

[christroutner]

There are some errors that get thrown by bch-api and thrown by bch-js that do not come through as an Error object.

The scope of this issue is to remain aware of these kinds of error. The solution is to fix the error handling to detect the err.error property, like done in these lines

} catch (err) {
  console.error('Error in transactions.js/get()')

  if (err.error) throw new Error(err.error)
  throw err
}