Pad to urlInterval in put_timeseries()

TimeseriesFactory.get_timeseries() pads to the requested interval with NaNs,
filling in start/end gaps. TimeseriesFactory.put_timeseries() is supposed to
do this (according to Jeremy Fee), but it was trimming NaNs from the start/
end before writing to file. This PR fixes this by using ObsPy's Stream.trim()
method, in a similar manner to TimesereisFactory.get_timeseries(), to pad to
the specified start and end of the urlInterval..

geomagio/TimeseriesFactory.py

@@ -226,6 +226,13 @@ class TimeseriesFactory(object):
                         trace.stats.location = new_trace.stats.location
                     url_data = TimeseriesUtility.merge_streams(
                             existing_data, url_data)
+                    # pad with NaN's out to urlInterval (like get_timeseries())
+                    url_data.trim(
+                          starttime=urlInterval['start'],
+                          endtime=(urlInterval['end'] - delta),
+                          nearest_sample=False,
+                          pad=True,
+                          fill_value=numpy.nan)
                 except IOError:
                     # no data yet
                     pass