Add developer mode that shows UUIDs of elements

[lukasrad02]

When using logging or inspecting objects during debugging, you often only see UUIDs of elements.

Therefore, it would be handy if the frontend can be configured to show element UUIDs in their popups or show the UUIDs by default when running in development mode (determine by NODE_ENV). If it is not determined from the environment, this setting should not have to be set every time the page loads but be persisted across page loads since the page reloads frequently during development.