Publish to NPM

Fixes https://github.com/angular-ui/ui-layout/issues/71

This does a few things. First, I added npm-debug.log to the gitignore, just a small accessory commit.
Second, it adds an NPM ignore, so when published to NPM, it doesn't include unneeded files, and only includes the license/readme/dist/package.json files. 

This means that by running npm publish (on master, generally speaking), it can first generate the compiled files and then publish them to NPM.

If it's more desirable, I can set up a publish npm task (akin to the bower one) that would let travis handle the building and npm publishing.