The list of `connectors` should also be parameter of the constructor

[justmoon]

When constructing a Client I should be able to pass in a list of connectors.

// new Client(pluginOpts, clientOpts)
const client = new Client( { /* ... */ }, {
  connectors: [
    // ...
  ]
})

When quoting, the connectors list should be chosen in order of preference:

• params.connectors (connectors passed to this specific call to quote)
• this.connectors (connectors passed to the constructor)
• plugin.getConnectors() (connectors as provided by the plugin)