On Site import, fill in missing site types from parent institution's type

The site import data is taken from https://docs.google.com/spreadsheets/d/1KtQNDTVaNBsodb-a4M_V89Damb0NJwpzNTVGq1gtx-4/edit?usp=sharing

Many of these sites don't have a site_type. We should be able to fill in these missing site_type's from the parent institution's type (see #358 (closed))