Added package file and gulp builder scripts

Things that changed:
- a package.json file, needed for npm modules (and for publishing to npm)
- a gulp builder

This gulp builder compile the coffee script to javascript, creates a minified version as well (including map files, useful for debugging), and creates a minified css file. Additionally, the gulp builder can up the pivottable versions, tag the branch, and push the version to npm and github.

A crashcourse.

One time:
- install npm, if you don't have that yet
- run `npm update` to pull all the builder dependencies specified in the package.json file (and needed for gulp to run)
- run `npm publish .` at least once, to publish your version to npm for the first time

Usage:
- run `gulp` to compile/minify js/css (this runs the 'default' task specified in the gulp file
- run `gulp [patch|minor|major]` to up the version, and push the lib to npm and github (haven't tested this fully, as for ownership reasons it is best if you do this. it should work fine though)

ps. The dist dir is now quite flooded with files. An idea to bundle the language files in single 'langpack' file? (these files are very small anyway)
pps. The minified css file might be a bit useless (css file is small anyway), but for consistency decided to leave it in anyway