Modify focus graph to include sample number.

Summary:
The sample number is rendered inside the focus v_graph point, so one can see
the order the samples were taken. There's also a bug fix to a qCDebug.

Test Plan:
Run autofocus, and look at the v_graph. Instead of little filled red circles with white borders, you should
now see (larger) red numbers indicating the order of focus samples, with white circles
around them. The first plotted point should show 1, the next 2, and so on.

Reviewers: mutlaqja

Reviewed By: mutlaqja

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D26251