Modified timeline to check for receiver column before filtering releases

 Changes to be committed:
	modified:   docs/notebooks/visual_detection_timeline.ipynb.rst
	modified:   resonate/visual_timeline.py

docs/notebooks/visual_detection_timeline.ipynb.rst

@@ -10,7 +10,7 @@ This tool takes a detections extract file and generates a Plotly
 animated timeline, either in place in an iPython notebook or exported
 out to an HTML file.
 
-.. warning::
+.. warning:: 
 
    Input files must include ``datecollected``, ``catalognumber``, ``station``, ``latitude``, and ``longitude`` as columns.
 
@@ -44,7 +44,7 @@ much for responsive than standard Scattergeo plot.
 
     from resonate.visual_timeline import timeline
     import pandas as pd
-
+    
     mapbox_access_token = 'YOUR MAPBOX ACCESS TOKEN HERE'
     detections = pd.read_csv("/path/to/detection.csv")
     timeline(detections, "Title", mapbox_token=mapbox_access_token)

resonate/visual_timeline.py

@@ -21,7 +21,8 @@ def consolidate_data(detections):
     """
 
     detections = detections.copy(deep=True)
-    detections = detections[~(detections.receiver == 'release')]
+    if 'receiver' in detections.columns:
+        detections = detections[~(detections.receiver == 'release')]
     detections['date'] = pd.to_datetime(detections.datecollected).dt.date
     detections['det_counts'] = 0
     detections = detections.groupby(