Upgrade Travis CI Badge to SVG. Add DavidDM Badges

Props totally go to @shinnn - though this should be a cleaner merge.

Using SVG Badges provides a clearer view for everyone (cough, retina display Macbookers... cough)
David-DM can be used to keep an eye on the npm dependencies that the project uses. The david tool from npm can also be used to automatically update dependencies listed in `package.json` to the latest version.