Numerous fixes

[Ambyjkl]

• Update all devDependencies, and most dependencies (did not update chroma.js in interest of bundle size, the thing gets even more bloated)
• Bump node version in travis config and nvmrc to 8.12
• Use uglify instead of babel-minify since a new version of babel-minify was not stripping license comments
• Remove full file paths from bundle (LOL)
• Few nitpicky changes to the app code (use prototype to share functions rather than using a closure)
• Add check for 'png' to the test

To clean up the diff, choose "Hide whitespace changes" in the diff view options

[qrohlf]

Closing because this is out of date and I don't agree with all of the changes made. If you'd like to contribute to improving the general architecture/build pipeline, I'd be glad for the help, but let's talk beforehand to get on the same page.