Implement default activity manager when native plugin is not on the class path

Once user puts native plugin on class path, he can manage activities via NativeActivityManager however when he does no put this plugin on the class path, after he injects AndroidDevice, he is not able to start activities because ActivityManager implementation is null.

In order to be able to start activities even when native plugin is missing, there has to be default ActivityManager implementation which does not uses WebDriver or Selendroid but it executes shell commands instead of that.

However, even after implementing this, it is questionable for what reason a user would start the activity when he can not control it by any means since WebDriver is missing and we can not inject it via Drone as well.