Build: Flatten dist directory on wet-boew-dist

See https://github.com/nschonni/wet-boew-dist/tree/e4fcbf08fe48834b0ba6435c5461bfa03f5c51b6 for the example of the new layout. Now that the demos live below the dist directory, referencing them using `dist/demos` seems like a bad url structure.
(Related to gh-2470)
I will add an index.html template as a separate pull