Output collection REM

For REM, if one animal viewshed crossing produces multiple photos, this should only be counted as one encounter.

For Distance Sampling, all photos (distances) are counted.

-> TODO:

• add ID to animals
• photos should also include this animal ID
• remove this to remove duplicates for REM application

Alternative:

• separate global photo data frames for distance sampling and REM, then just remove duplicates when tick_picks are appended. Requires no Animal ID