Read package metadata from meteor-package.js

... instead of package.js. Meteor-core thread:
https://groups.google.com/forum/#!topic/meteor-core/-qbP-ttPLS8

TODO: the following files need review in particular:

* tools/tests/old/cli-test.sh
* tools/bundler.js, lines 2041-49
* scripts/admin/jsdoc/jsdoc-conf.json
* tools/package-source.js. lines 453, 858
* docs/client/data.js needs to be regenerated

`package.js` files throughout the repo should be `git mv`ed to `meteor-package.js`