As an end user, I want to be able to add and remove widgets on the dashboard, so I can get different insights on my data

[cwulfman]

To add a widget to the dashboard, the user must be able to select from a list of available widgets.

Torchlite must maintain a registry of widgets; the registry must be well-documented for end users: A summary of the widget's functionality; a description of any algorithms it applies to the workset data; a link to the code so the user can inspect it.

[x] On the back end, when the user adds a widget to the dashboard, the app creates an instance of the widget, with a unique id, and notifies the front end that the widget-list has changed. The back-end part of the widget does not perform any calculations until the front-end asks for data. When the user deletes a widget from the dashboard, the back-end removes the widget from the dashboard's widget list, and tells the front end that the widget list has changed.

[jswatsch]

HTRC: this seems described correctly and is essential.