define Character and add relationships of it
Temporary workaround for import_all_modules

This should be fixed.
Return as frozen set
Test comply
Merge pull request #58 from tkiapril/import-module-workaround

Temporary workaround for import_all_modules
avoid using backref for relationship
migration script for Character and WorkCharacter
Merge pull request #56 from sjw0687/character

Add character to ontology database schema