New Chart.js.zip package

Samples need to be packaged with built libraries (which one have been removed from the repository), so create a new `gulp package` task to generate a ZIP archive with dist files, samples and the license file. This archive is generated in the ./dist/ folder and will be deployed by Travis along the GH release. Note that the ./dist/ folder is not preserved but merged in the archive root. Also change samples requiring moment.js to load this lib from the CDN instead of the ./node_module folder.