implement browser.getConsoleLogs(logLevel) and browser.capabilities

**browser.getConsoleLogs(logLevel)**

If you call `browser.getConsoleLogs()`, you get all log events from the browser since the last time this method was called or a page was loaded. If you specify a logLevel, you get only that level of log events. Specifying a logLevel does not clear all log events of other levels. Testium caches those events to work around this possible issue with WebDriver.

**browser.capabilities**

The [capabilities object](https://code.google.com/p/selenium/wiki/JsonWireProtocol#Capabilities_JSON_Object) returned by creating a WebDriver session is available on `browser.capabilties`. This can allow you to alter tests based on which browser they are running. For an example in this very repo, check out the dialog tests. They are all grouped as one pending test when running the suite in phantomjs because it doesn't handle alerts properly.