Split package content and some revision to day one of activity

@BernhardKonrad Please review and merge. I've got to do other stuff for a while but will check back in later today.

I assume you'll rationalize the Imports RCurl thing as discussed via email.

My main suggestion for improvement is this: on Monday, I think we didn't model a realistic workflow. For example, we didn't test individual lines of `gday()` interactively. We didn't test the `gday()` function as a whole interactively. We didn't use `devtools::load_all()` to emulate build and loading the package. I think we need to do more of that stuff, because that's what real life is like.

Also, let's call the main argument `team_name` or, even better, just `team`. All course materials are sort of converging on using the underscore `_` as word delimiter.

You can count on me to say more about source vs bundled vs binary vs installed vs in-memory and the `devtools` and base tools for moving between those package formats.