add error checking when loading shapefiles

ogr2ogr error
```
FAILURE:
Unable to open datasource `/path/to/shapefile.shp' with the following drivers.
```

User needs to check location and names of shapefiles on disk.


SQL errors
```
ERROR:  column "geom_900921" of relation "acs2016_5yr_bg" already exists
```

This happens if the shapefile was already loaded in.