C++: First Qt-based GUI for Test Beam Run Control

This MR introduces a first graphical user interface targeting the control of a Constellation in a testbeam context. The UI is modeled after euRun of the EUDAQ framework. This requires !179 (merged) to be merged as it provides the base component for controllers.

Features include:

• Parsing & distributing TOML configuration files (see #34 )
• Listening to heartbeats, automatic update of remote states
• Distribution of commands to all endpoints
• Automatic incrementing of run number (run identifier is string plus sequence)
• Possibility for the operator to send log messages on any level
• Display of the run duration
• ...

Individual commands can be called from the context menu of each satellite:

Responses are rendered as string. If the payload was a dictionary, the key-value pairs are displayed as list:

States in the connection list are colored: