Tango Controls tracer and visualiser

This feature's goal is to provide a product that is able to visualise Tango Controls Device program flow in near realtime.

The product would:

• Subscribe to the TC logging system and evaluate logs which are output by the `@DebugIt` decorator. The `@DebugIt` decorator inherits from the `tango.LogIt` base class.
• Collect matching entries of `@DebugIt` entry and exit logs.
  • In the case that the logs which are generated by the `@LogIt` base class cannot be distinguished, extend the decorator base class `@LogIt` to generate and output a unique ID which then allows combination of entry and exit messages.
  • Display the entries in a way that allows visual or computerised tracing of command flow in Tango Controls Devices.
    • Visualisation should be modular.
      • Different output modules should be allowed for each tracer process that is executed.
      • If implementation allows, different output modules can be allowed at the same time for each tracer process.
      • Three output modules are foreseen to be needed:
        • Visualisation on command line in human readable form. Perhaps some for of indentation could be used to highlight calling hierarchies?
        • Storing the command flow to a file for automated post-processing.
        • Visualisation in a web GUI with realtime updates.
• For future extension, allow different input sources.
  • For now it is only the `@DebugIt` log but it is envisioned that tracing and visualsing of Device states, adminMode or obsState will be traced, too. It is understood that tracing attribute values requires different techniques than tracing commands.