tmf: Improve histogram responsiveness

tmf: Improve histogram responsiveness

The Histogram had its own kind of throttling TimeRangeSynch signals,
but simply freezing itself for ~100 ms, which would of course imply
no other time range could be selected.

Replace this with the fancy new signal throttlers. Now the
histogram display gets updated right away, while the background
time range updates and queries only happen after a short time
without any new time range selection.

The user experience should increase a great deal!

Change-Id: I89a872d9d829d5522523912f73dca2c31f48e64c
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/11503
Tested-by: Hudson CI
Reviewed-by: Bernd Hufmann <bhufmann@gmail.com>
IP-Clean: Bernd Hufmann <bhufmann@gmail.com>
Tested-by: Bernd Hufmann <bhufmann@gmail.com>