Refactor to require assignment of code to asana ID

[kalleth]

Our hubot communicates via HipChat, which uses different short codes to
refer to people other than their full names. For example, to assign a
task to me, I would do:

todo: @trussell Do something soon please!

I've refactored to require first telling hubot which asana ID maps to
which 'person', rather than attempting to do fuzzy-finding (Which
didn't work for our case).

You assign like:

@hubot todo alias 1251251251512 @trussell

And you get the asana ID of the users by doing

@hubot todo users

I've also adjusted the constants default values to be more meaningful,
and fixed error reporting for the latest version of the Asana API.

[kalleth]

As we only use Hipchat, I'm not sure how nicely this will translate to other host services. Sorry if it's a bit hipchat specific.

[kyleknighted]

There is a merge conflict - could you resubmit?

[dylanh724]

Did this ever get merged? I use hipchat as well