If we don't have a minute worth of input, we should shrink the
visible area to exactly what we came across.
We still have the issue of the UI creating the capture file
before auth has completed, but we can fix that later so we
have a "semantically" correct start time.
These signals are emitted when a visualizer row has been added
or removed from the view. This might be handy if you want to
resize a paned based on the natural size of the visualizers.
This adds a new helper widget SpVisualizerView to simplify using
visualizers from applications using libsysprof-ui-2 such as
Builder.
We can manage the view range, zoom, etc from this widget going
forward.
