Media Keys working

Please see the README for enabling macOS permissions.

As raised in #26

Track & Artists Notification improvements

Fetching & Cleaning Track meta correctly

 - small CSS adjustments to the mixcloud site for the macOS window controls
 - pinning package version numbers
 - Closes #18

Auto Update

• auto update (checking against new versions on GitHub Releases)
• reverted to npm from yarn
• removed webpack (file structure simplified)
  • no hackery between local electron and build
• much increased security (no node.js in webview)

Bug Fixes & Code Trimming

• Removed Analytics tracking + packages (not cool, esp. without a Privacy statement)
• Removed (non-working) Preference window
• Removed React and all it's bulk
• Removed a few other unused packages
• Fixed JS error on notification click
• Added Docker-compose file and instructions for cleaner/safer development
• more meta data in the package.json