Add connection status to Dashboard and Resources->Agents view

Current Situation

• The Controller reports the Agent coupling status (coupled, reset, resetting, shutdown) and it reports problems such as connection refused, missing heartbeat etc.
• Occurrence of a problem makes the GUI paint the Agent connection status in red color.

Desired Behavior

• The API provides more detailed information about the type of problem:
  • Temporariy problems such as missing heartbeat that will not require user intervention. Typically such problems are resolved within a short period of time.
  • Permanent problems such as connection refused, that require user intervention.
• The GUI makes following use of text and colors:
  • The text displayed indicates the coupling status: coupled, reset, resetting, shutdown.
  • Olive color indicates a temporary problem.
  • Red color indicates a permanent problem.
  • Grey color indicates an unknown status, for example if no active Director Agent is available in an Agent Cluster and cannot report the status of Subagents.
  • A tooltip is available that indicates the problem message.