Introduce setEmulateMedia so that we can emulate print css for example

[aml11]

Also add a way to send parameters to chrome launcher (we need it to be able to run headless-ly and with extensions enabled for some scenarios.
For example, in order to create a pdf with setEmulatedMedia("print") we will create chromeless like this:

const chromeless = new Chromeless({chromeFlags:[
        // Disable built-in Google Translate service
        '--disable-translate',
        // Disable all chrome extensions entirely
        //'--disable-extensions',
        // Disable various background network services, including extension updating,
        //   safe browsing service, upgrade detector, translate, UMA
        '--disable-background-networking',
        // Disable fetching safebrowsing lists, likely redundant due to disable-background-networking
        '--safebrowsing-disable-auto-update',
        // Disable syncing to a Google account
        '--disable-sync',
        // Disable reporting to UMA, but allows for collection
        '--metrics-recording-only',
        // Disable installation of default apps on first run
        '--disable-default-apps',
        // Mute any audio
        '--mute-audio',
        // Skip first run wizards
        '--no-first-run',
        '--headless',
      ]
    })