Add compatibilty with jspm and SystemJS

[gsontag]

It's an update I made for a private project, but the only way to work with jspm dependency management and systemJS loader, because moment.js didn't create global when loaded by systemJS.
There is two modification for work with jspm:

• Add jspm dependencies informations in package.json
• Add a hook in js files to check if global exists and load it if not.

PS: replace the pull request initially made from my master, appologies