Implement root capture identification algorithm

[ZavenArra]

Idea: The location of a capture may intersect with the convex hull of one or more session segments. Taking a list L of session segments with convex hulls that intersect with the capture location, if the capture is attached to the session segment in L with the lowest start time, then it must be a root capture. A root capture is the first tracking of a given tree in our database.

Algorithm:

captures_to_process = all unprocessed raw captures with session_segment != NULL
AND root_check_processed_at = NULL
for each raw_capture as current_raw_capture
L = set of all session_segment with convex hull intersecting raw_capture.location
first_session_segment = session_segment in L with earliest start_time
if raw_capture.session_segment_id = first_session_segment.id
set raw_capture.root = true
set raw_capture.root_check_processed_at = now