Resolve "PostAnnotator: Keep Selected Person/Bodypart when jumping in video"

Closes #2019 (closed)

• Selection of Person/BoundingBox or Skeleton/Bodypart should now persist when changing video position
• if the Selection is invalid at the new video position, the chip under post annotator input will dim and show a "!"
• if an Annotation with invalid Selection is sent off, the invalid Selection will not be included in the Annotation
• when entering text for an Annotation, the Selection is locked and will be sent (NOTE: in this case the overlay of the Selection in the video at the time of sending might not represent what will be saved if the video position changed after input began)
• if entered text in the input is cleared, any existing Selection will be unlocked and checked for validity again
• also contains an updated Kinesphere Lane where »Follow Selected User« now works as expected