Updates to Webpack

Reconfigures ddm-dropdown to use webpack to compile all the assets used
by dropdown into a single JavaScript file. This includes the necessary
CSS. It also allows us to distribute the file in a UMD format.

Changes build process from gulp to webpack where possible.

Splits dropdown.js into three separate files in a components folder
that uses require to bring in necessary dependencies.
Updates Webpack Build to Minifiy

Changes the webpack build step to always minify and slightly reorganizes
the webpack.config.js how the loaders work for scss files to be less
brittle.
Merge pull request #4 from deseretdigital-ui/webpack

Updates to Webpack