Update styles to be more platform-agnostic

[ryanscottaudio]

• [x] Update method of parsing styles to more closely mirror React Native
• [x] Export this method so it can be used in other repos to convert Story JSON styling to React inline style JSON
• [x] Refine style flowtypes
• [x] Export flowtypes
• [x] Stop enforcing video MIME-types to begin with video/; only prepend that if necessary
• [x] Add vendor prefixes