Add a Custom tab to Dashboard for Stats / Metrics widget

[smlambert]

I think we can rename and repurpose the FVT tab to a Custom tab, and make it a space where we can create a new Test Metrics and Stats widget and drop it into that view help us track project stats.

A Custom tab view is one that people can 'personalize' as their selection of widgets in their view is remembered (via browser cookies). Reset button gets them back to the set of default widgets in a view.

Custom creates a location for potentially other widgets to be written and dropped in, focussed on things that may be helpful for daily tasks and tracking.

[smlambert]

FYI @andrew-m-leonard