Create animation "on demand", that is, when there is at least one animated progressbar.

Delete it when all animated progressbars have stoped or have been unregistered.
This prevent the underlying QPropertyAnimation to be deleted "too late" after an application was exited,
which in turn sometimes result in a crash
CCBUG: 356940
changes. Lines starting # with '#' will be ignored, and an empty message aborts the commit.