Updated Tracker
Added basic implementation for Google Analytics tracker
API updated
Comments addressed.
Merge pull request #669 from anserran/ga

Basic implementation of user tracking system (using Google Analytics)
    Added ConversationSystem, DialogueSystem

    - ConversationSystem processes a TalkComponent, which is added by
      TriggerConversation effects. They are display-independent.

    - DialogueComponent processes DialogComponents, which can specify
      callbacks. Currently they all have the same style; this will
      be addressed in later commits.
Added ConversationDemo

Click on dialogues to choose / dismiss them.
Add a components.dialogue package, systems.dialogues package

Since there are now two types of dialogues (menu and line)
Cleaner, call-back free conversations.

Conversation advancement is done via polling. Removed logging.
Small bugfix in Selection
Merge pull request #664 from manuel-freire/conversation-support

Conversation support