add community repository

requirements.txt

src/sakia/data/entities/__init__.py

src/sakia/data/entities/blockchain.py

src/sakia/data/entities/community.py

src/sakia/data/processors/communities.py

src/sakia/data/repositories/__init__.py

src/sakia/data/repositories/communities.py

src/sakia/data/repositories/identities.py

src/sakia/data/repositories/meta.py

src/sakia/data/repositories/meta.sql

src/sakia/tests/unit/data/test_communities_repo.py