Per-Sender Settings in Observatory

This MR exposes the per-sender and per-topic subscription mechanism to the UI:

Features:

• Senders are automatically added & removed if they OFFER or DEPART via CHRIP, not limited to satellites.
• Automatic topic update when new topics are announced via CMDP or by receiving a log message
• Expandable topic lists, click on sender name to open all topics individually
• Only one topic list is expanded at the time, selecting another will collapse previous one
• Colored ComboBoxes for log level selection, provided as independent widget.

Open items:

• When new topics arrive, the current ones are replaced - but their subscription state is lost. Need to think how to keep that
• The alignment of the QTableView of the topic list is not correct yet, it should be right-aligned.
• We need to define how to deal with the deluge of Qt raw pointers since this doesn't use a UI file but does the layout manually.