Fix npm/browserify usage

Other plugins are doing `define('scribe-common/element')`, so for this to work in npm/browserify then we need the `element.js` file to be located at the root of the repository.

Also set the `package.json`'s "main" to `element.js`, since there is no `scribe-common.js` file, and `element.js` appears to be the only JS file in the repo at the moment.