Refactored filter construction to _constructFilterForProjectSelection.
This allows Grading Project Survey to overwrite this method and create its own filter.
# Getting the normal admin routines, classes, and `site` instance.
from django.contrib.admin import autodiscover, site, StackedInline, TabularInline, HORIZONTAL, VERTICAL
# Geographic admin options classes and widgets.
from django.contrib.gis.admin.options import GeoModelAdmin
from django.contrib.gis.admin.widgets import OpenLayersWidget
try:
from django.contrib.gis.admin.options import OSMGeoAdmin
HAS_OSM = True
except ImportError:
HAS_OSM = False