Refactor to CoR

Epic pull request is epic.

This PR attempts to refactor the existing Skypebot to make use of command objects. The main handling of Skype command words (USER, CHAT, etc) is done using a chain of responsibility pattern implementation. The advantage of this is a thinner core engine, and easier overriding of the command behaviours.

Within the handler that controls CHATMESSAGE commands is a further, looser implementation of chain of responsibility to handle chat message contents. The main advantages of this over the existing closure implementation is easier testing and a more flexible plugin system. Also, multiple handlers can now react to the same message, so that 'special case' rules can be added as message handlers instead of being part of the chat message handler itself.

The unused web interface is removed. The functionality this provided will be replaced in a future PR based on chat messages.