Publish packages for each individual API.

Problem

This is going to be done in several steps: - [x] Re-organize the directory structure to map to individual modules (#1167) - [x] Setup and publish a `googleapis-common` npm module that just contains shared bits that will be used by all packages - [x] Generate a package.json for all of the individual APIs - [ ] Script the `npm publish` process so that each individual package is published along with the larger meta-package These steps are of course subject to change as we discover things through the process :) --- UPDATE --- We're down to the last step of actually publishing the individual modules. @alexander-fenster, @jkwlui, and @JustinBeckwith last got together to chat about this, and came to a few conclusions: State of the world today - We decide when to run the generator in a somewhat ad-hoc fashion. As someone asks for a release, we cut it. - We run the generator by having a developer clone the repo, run `npm run generate`, and then submitting a PR with like 1344247584 changes. - After checking in that PR, someone has to submit a new release with releasetool. This will create a new tag. It is almost always semver major (see the fact that we're on v38). - The generator is somewhat monolithic. It works by blasting away the `src/apis` directory, and re-creating every API from scratch every time. This makes it easy to detect new APIs, and easy to detect removed APIs. Where we need to be - We want a bot that runs the generator(s) nightly. We should use `synthtoo