Drop Bower support

[robneu]

It seems that Bower usage has dropped off quite a bit and we should be able to accomplish the same thing by installing via npm. I'll need to look into it a bit, but I don't think there's any reason we can't just install our bower dependencies as npm dependencies and move them into the correct location from node_modules.

It's less commands to run when setting up a theme build and less config files to maintain. Seems worth it if it doesn't break anything...