timing: optional terse format for timing annoations

timing: optional terse format for timing annoations

In some situations (inspecting a dense run of pulses in a burst of data
communication) it takes a lot of zooming before the 'timing' decoder's
'time' annotations start revealing numbers. Which limits the number of
pulses which can fit in the visible trace area.

This is a stab at improving the usability of the timing decoder for
similar "crowded pulses" scenarios. Try to come up with an annotation
text that is shorter yet communicates the very details which the user
needs in this situation. Drop the frequency, avoid umlauts in the unit
text, don't use decimal places (use all integers within a scale). Even
offer to drop the unit text, assuming that a dense run of pulses results
in all times sharing their scale.

Make the terse presentation optional and off by default, and use a
separate annotation class for maximum backwards compatibility.