Better error message saving livelihood activities - see HEA-925

Add a try .. except block around the code in get_instances_from_dataframe
so that it is clear which Livelihood Strategy is the source of an error. Previously
an error finalizing a Livelihood Strategy and its Activities was reported using
the label and row number of the subsequent Livelihood Strategy because
the previous Strategy isn't finalized until after we start processing a row that
has `is_start == True` which marks the beginning of the next Strategy.

Author: rhunwicks