Doing otherwise will result in the gun data file
appearing has having been read, but no data will
have been saved as there was nowhere to save to.
Fixes#29.
Each of the save_* operations starts a transaction
(which is automatically commited if all goes well).
The main reason for this is to ensure that by the
time raw_lines and final_lines events fire, the
corresponding entries in raw_shots and final_shots
have already been populated.
Provided that the SmartSource headers are being
saved to file, and that the path to those files
is present in the survey configuration, we now
import SmartSource information as metadata in
raw_shots.meta->'smsrc'.
Closes#19.
It will not delete any labels that have been removed
from the configuration, as those may be used, but it
will add new labels and modify existing ones if they
changed.
