Added API + package manager + global igloo command + helmet + gulp (with bunch of plugins)

Details about all the changes except removal of Gruntfile.js are in commit messages. (added Gruntfile.js to an empty package since the user will probably need either Grunt or Gulp, not both. Grunt version of Gulp script can be found [here](https://gist.github.com/markgoodyear/8497946#file-gruntfile-js))

Details about new package manager can be found in /packages/readme.md. Didn't update main Readme.md expecting zero merge conflicts (with the changes you've made there), but oh well, I see there are a few.

In short, this is how I tested package manager:

``` bash
$ cp -r * /usr/local/lib/node_modules/igloo
$ igloo create ~/myapp helmet
$ cd ~/myapp
$ igloo remove helmet
$ npm i

# ran node igloo and checked the site in the browser at this point

$ igloo add gulp
$ npm i gulp -g
$ npm i
$ gem install sass
$ gulp
$ gulp watch

# opened a new tab, ran node igloo, checked the site in the browser,
# should make some changes to background color and font weight.
# and of course, tested installing LiveReload :)
```

Sorry, this became a massive pull request, thought I could avoid merge conflicts :D