Removed extra commas, easier child theming

[grantnorwood]

Removed extraneous commas from gruntfile.js. Split out the off-canvas menu and top bar into layout parts for easier customization from a child theme.

[Aetles]

Why remove the commas? Having them there makes it easier to cut and paste lines without having to adjust commas and reduces risk of missing comma errors. Look at the example code here, all trailing commas: http://gruntjs.com/configuring-tasks

[grantnorwood]

You're probably right, @Aetles. It's my habit for writing js that's backward-compatible with older browsers, and since I noticed not all object literals in that file had trailing commas I just made it consistent. As node/grunt use a modern version of ECMAscript that supports trailing commas, it wouldn't be terrible to leave those in.

Feel free to make that change and submit a pull request!