ptz: Recall preset when face has lost

[norihiro]

Description

When face has been lost, call preset on the PTZ camera.

How Has This Been Tested?

• [x] To avoid going to the preset at short lost of the face, timeout might be implemented.
• [ ] Test libvisca backend
• [x] Test obsptz backend

General checklist

• [x] The commit is reviewed by yourself.
• [x] The code is tested.
• [x] Document is up to date or not necessary to be changed.
• [x] The commit is compatible with repository's license.

Close #53

[norihiro]

Maybe it would be better to slowly zoom out before recalling the memory.

[norihiro]

The preset is recalled even when the tracking is paused, where it should not be recalled.

[wwboynton]

Will a build be released with this PR included soon? Or should I build it myself?