Remove HipChat#developers and ChatClient#developers.

[ashercodeorg]

An alternate approach would be to rename developers to message_server_operations. However, this seems inferior, as it encourages a proliferation of such aliases.

[aoby]

It does seem a little cumbersome and prone to misspellings to pass 'server operations' to every call. Since all the messages are currently going there, perhaps we should set that as the default room and make room an optional named parameter?

Then the common call (every one currently) would be simply ChatClient.message 'my message', and we wouldn't need any aliases.

[ashercodeorg]

Not all the messages are going there, we use lots of other rooms in HipChat#message. That said, I like the suggestion of a default room, let me do that.

[ashercodeorg]

For convenience, also as it seems tangential to resolving the TODO, I'm going to do the default room in a separate PR. Also, that way I can add the default room after removing users of HipChat (would prefer to not need to make that change twice). And I can do so after adding tests to ChatClient and Slack.