Add some rudimentary CSS styling to the buttons.

Also bump up the base font size to 150%.
Sort paths in from/to dropdowns.
Use MB instead of bytes.
Add framework for sync* callbacks.
Add confirmation of sync* operations.
Convert error console.log calls to alerts.
Stop relying on console.log messages.

Mobile Chrome on Android gives no access to the console.log messages.
We either need alerts on status via the UI.
Remove dummy development code.
Improve formatting and readability.