Mark Empty Conversations

[Enthalpy]

Cross-examinations and investigations consist of a series of conversations, which are currently separated in tabs. It is proposed that each conversation which can be filled but is currently empty has a marker on the tab to denote this, so it's easier to spot uncompleted sections of the event block.

Assuming this feature is planned to be implemented (it could be distracting for intentionally empty sections, and demand doesn't appear very strong), we need to decide what marker we'll use for this.