Grunt fixes

This removes the `grunt-concurrent` task as it did not provide a significant enough performance improvement to be worth the overhead.

This also adds a `grunt develop` task that does essentially what `grunt build` does, but without minifying assets.

Modernizr was also added to the copy task so that it would be included when building and deploying a project.

Also, `_base.html` now actually uses the `{app,libs}.min.js` js files rather than `{app,templates,libs}.develop.js` when building for deployment.