Added basic stylesheet and error view, made code style consistent, fixed playfile crash when no access

- added basic error template and global stylesheet
- made listenPort a config var rather than being hard-coded, moved config vars to top of server.js with a comment explaining they could/should be changed
- render a helpful 404 error when given media_path not found rather than crashing
- fixed crash when ffprobe cant stat file for playfile view (e.g. due to insufficient perms): now passing dummy obj with empty streams array rather than undefined ref which crashes renderer
- add data-cast-api-enabled=”true” to html tag of playfile page per Google recs
- made all line endings and string encodings consistent (e.g. replaced unnecessary double-quotes with single-quotes, add semis at end of lines without them)