Support blink based Opera natively

[OndraM]

The library is currently missing support for Opera-Blink browser.

To starting on the remote remote server we miss the constant operablink for browser name - but this could be worked-around as in #343:

$desired_capabilities = new DesiredCapabilities();
$desired_capabilities->setBrowserName('operablink');
$desired_capabilities->setCapability('chromeOptions', ['binary' => '/usr/bin/opera']);

We should also support starting operadriver directly, without selenium server. So new OperaDriver and OperaDriverService should be added (similar to their Chrome counterparts).