Add support for census table

[lucernae]

• Add external module to fetch census from Kemendagri Indonesia
• Add fixtures:
  • census table
  • census_kemendagri table as external module
  • census_kemendagri trigger and trigger functions to populate census table
  • flood intersections mv for population
• Add helper scripts:
  • ArcGIS REST API Wrapper to fetch dataset
  • Scripts to fetch data from Kemendagri Indonesia
• Add unittests:
  • Add backend unit test for population
  • Add helper scripts unit test for census_kemendagri
• Add test dataset:
  • Add clipped census data for census_kemendagri