v0.3

Changes:

• Introduce chat history support
• Add support for the slixmppd backend
• Rename Buddy List to Conversation List
• Introduce multiple backend support
  • Each backend is listed as conversation in the Conversation List
• nuqql command window is now also a conversation in the Conversation List
• Coding style fixes and code reorganization
• Requires purpled v0.2 or nuqql-slixmppd v0.1.