We're not including anything above `main.js.in`, so the top of that file
always ends up as the top of the final user script. We don't need a
separate build step to include it.

Forgot to comment out the Mousetrap license in the final build file.

This was for debugging and is no longer needed.

This is no longer needed now that Peniquitous is a Greasemonkey user
script.

Now that we've added Mousetrap via NPM, we can remove the one we
installed via Bower and Bower files.

Didn't really need to switch to NPM, but I wanted to get a Mousetrap
dependency that included its LICENSE file so I could include it in my
build.