title: Adding new Capability on runtime to appium driver after its being instanciated
body: <p>is it possible to add new capability to Appium driver (Android &amp;/IOSdriver) after driver's being instantiated?
  Or are there set of capabilities that could be added</p>
  
  <p>Also, is it possible to achieve the same for Selenium's remotewebdriver.
  Thanks</p>