Add an AnalogFrame widget

This is GtkFrame subclass that allocates enough space for a
circumscribed circle around its child and draws it.
It will be used as a base class for drawing analog progress in stopwatch
and timer.
Add analog progress to the timer

Add a circle around the timer showing the analog progess of the the countdown.
Add analog progress to the stopwatch

Add a circle showing the stopwatch activity.
This patch also ports the stopwatch to GtkListBox and changes the layout of the panel
to put the lap list on the side.
Experiment with smaller analog frames

Try smaller fonts and padding, linked buttons to save space.
Implement blinking in the paused timer

The implementation is done with CSS so that we can tweak it or do neat
things like turning it off in backdrop.
Use different css classes for the time labels

This gives us more freedom in each panel
Put margins around the laps list
Use an ui template for the stopwatch