[Epic] Target Dashboard

[andrewazores]

Currently the main/default "Dashboard" view is completely empty, other than a TargetSelect widget. This should be populated with some information about the target itself (JMX URL, alias, labels, annotations), as well as some widgets showing some high-level information about some select metrics. This could include some charts of timeseries-like JFR event data, or automated analysis reports scores. Ideally, the user can configure the layout and content of these widgets within the Dashboard, and this layout is reused for all targets and the layout information persisted for the user's next session.

• [Story] Dashboard Card implementations #838
• [Story] Dashboard contents/layout should be configurable #727
• [Request] Notify user when dashboard cards cannot be loaded #876
• [Task] Handle "no target" selection on Dashboard #883