Changed shortcut for screenshots yet again to CTRL+F

Previous conflict with Plot.

Signed-off-by: Nicola Ferralis <feranick@hotmail.com>
Added Clear Plot button. Changed workflow for restarting acquisition.

Restarting now does not clear the plot and leaves the plot window open.
This is to allow the user to decide if the plot needs to be cleared or not.

Signed-off-by: Nicola Ferralis <feranick@hotmail.com>
Do not plot if no acquisition has been run (and the image is opened).

Signed-off-by: Nicola Ferralis <feranick@hotmail.com>
Updated Changelog.

Signed-off-by: Nicola Ferralis <feranick@hotmail.com>