adding specs for HipChatMessage exposed some issues with the way I was
building the matrix-commit style notification message, so it ended up being
quite a bit more changes than I expected.

The save call from the service configure form submits an empty string as
the server URL if left blank, which I've indicated to do in order to use
the default server, but Hash#merge will happily overwrite a full string with
a blank string if asked, so we need to break that out, along with the worker
options which get mutated into string hash keys, of which the HipChat client
seems to not understand. Additionally, add another spec to make sure we call
the Sidekiq worker with expected arguments.

    * Move existing Slack service spec into a subdir, mirroring /app
    * Wire up HipChat service to the project and services controller.
    * Split the message building into own class.
    * 'namespace' room and token variables.
    * Enforce v2 client (bug in HipChat gem v1.5.0. fixed in 1.5.1). Note
      that I'm using the same version string as GitLab-CE, for shared
      installations.
    * Defer execution to a notifier worker, like the Slack service.
    * Ensure passing specs (basically a Slack service spec copy, fwiw)
    * Added change to the CHANGELOG