Added a SeedIds array to the output of stream tracer.

The SeedIds array is a cell array that contains the ids of
input seeds for each polyline in the streamtracer output.
This can be used to identify which streamline came from
which input seed.

Change-Id: If045716a4b7a19d02f26d16d25864b5f7fbb3a38
Merge topic 'add-streamline-seedids' into master

07b7459d Added a SeedIds array to the output of stream tracer.