New flow to retain all of the other folders within public/assets

- [x] @Attamusc 

The problem that prompted this change is that new images (added after our build change) weren't being optimized and included in `public/assets` after the `swap` task. This happened because I only carried the `css`, `templates`, and `js` files between the steps of the build process.  This PR addresses that.

The new flow:

* Copy all of `public/assets` into `public/assets-ugly` (4 to 7 second perf hit)
* Do an in-place, parallel uglification of `public/assets-ugly/js`
* Do an rjs build from `public/assets-ugly` into `public/assets-built`
 * Cannot do an inplace bundling due to conflicting `common` bundle name
* Copy the rjs built assets from `public/assets-built` back to `public/assets-ugly`
* Swap `public/assets` with `public/assets-ugly`