Provide a higher level API for asserting against browser console log

[dkarlovi]

See #339 (comment)

1. works only on Chrome currently (not sure if that's state of the art)
2. needs a nice way to request the capabilities when creating the client (maybe can be auto-requested?)
3. needs an API to assert against the console content, which is
   list<array{level: "INFO"|"WARNING"|"SEVERE", message: string, source: "console-api", timestamp: int}>

Initial API proposal

$this->assertBrowserConsoleSevereLogIsEmpty();
$this->assertBrowserConsoleInfoLogContains('hello world');