Need to load segments in 3-simple-dsms.Rmd; also reload sightings

[jjrob]

When https://github.com/DistanceDevelopment/spatial-workshops/blob/master/exercises/3-simple-dsms.Rmd is run, the afternoon of the second day, this will be the first time that segments will exist. We will have created them in the morning of the second day.

3-simple-dsms.Rmd should be adjusted to:

• Load the segments, rather than relying on the earlier scripts (1 and 2) to have done it. Those earlier scripts cannot do it because the sightings did not exist yet (see #32, #33).
• Reload the sightings. They will now have a SegmentID field, that they did not have on the first day of class. We will have created and populated it in the morning of the second day (see #32 and #33 again).

[dill]

So I covered this a bit in my response to #33. I'll hold off on this until you look at that.

[dill]

Copying the previously fitted df-models.RData into the Exercise_Day2.zip directory, then running process-geodata.Rmd lets 2-simple-dsms.Rmd run with no issues.