Feature/fix require cache

[michaellopez]

This fixes the instances where changes to CSS and JS causes a new manifest file to be written but not read back properly in the build process causing the site to break. This is due to the fact that require caches any successful file loads.

Edit: This PR also includes a change that allows filenames to include the string "site" and "page". Without this fix the build ends up ackward and incomplete with a file named "subpage.js" for example.

[michaellopez]

Sorry meant for this to end up on our fork, but leaving it here in case @moudy surfaces again and wants to continue Broccoli Taco.