Rewritten from the ground up using ES modules and trying to separate the UI from the core functionality.

[dom111]

• Rewrote code and organised into ES modules.
• Remove jQuery dependency (#30).
• Add keyboard navigation.
• Switch WebDAV test container to Alpine Linux.
• Add eslint for code style validation.
• Add karma/jasmine for testing.
• Add .babelrc.
• Add some basic unit tests.
• Rework package.json scripts.
• Add Webpack for building.
• Remove inlined external assets to resolve as module dependencies.
• Update document title on navigation
• Add toasts to notify of errors (#49).
• Add .gitattributes file to avoid CSS being counted incorrectly on GitHub.
• Add EventObject class for handling events within the UI.
• Add a check (HEAD request) before trying to show images, fonts, videos, audio to prevent invalid lightbox from showing up.
• Update .editorconfig.
• Add stylelint.