Dashboard widget stucture and QS messages widget

As an API user I want to be able to choose one or more predefined widgets and attach it to my application dashboard.

Similar structure to Diagram should be used. There is main DashboardWidget entity that contains common properties, and property content provides data by different strategy for each type of widget.

In this ticket, also the widget type QSMessages is implemented.

AC

• Entity DashboardWidget is added (https://confluence.digitalearth-hgf.de/pages/viewpage.action?pageId=16716827) - fields marked with RO are read-only and are no part of persistence
• User - DashboardWidget are related in 1 to many relation
• When DashboardWidget is queried, fields marked with RO are generated based on diagram type (DashboardDiagram.type field)
• Widget type QSMessages is implemented:
  • last 10 QS messages - QSObseravion.qsComment from last 10 QSObservation entities that the user can see
  • dataSeries JSON format:

    [
          {"qs_observation_id": 1, "comment": "Message 1"},
          {"qs_observation_id": 5, "comment": "Message 5"},
            ...
    ]

• Tests

Review

• Entity DashboardWidget is added (https://confluence.digitalearth-hgf.de/pages/viewpage.action?pageId=16716827) - fields marked with RO are read-only and are no part of persistence
• User - DashboardWidget are related in 1 to many relation
• When DashboardWidget is queried, fields marked with RO are generated based on diagram type (DashboardDiagram.type field)
• Widget type QSMessages is implemented:
  • last 10 QS messages - QSObseravion.qsComment from last 10 QSObservation entities that the user can see
  • dataSeries JSON format:

    [
          {"qs_observation_id": 1, "comment": "Message 1"},
          {"qs_observation_id": 5, "comment": "Message 5"},
            ...
    ]

• Tests