Pass DB instance from validators to field types (ref #32)
Test relation types (ref #32)
Revert "Pass DB instance from validators to field types (ref #32)"

This reverts commit f5af91361ce186808147b2aa6c0020b1b5dc6614.
Give access to database instances from backend
Use global_registries to access database instance from backend
Merge branch 'dev' into add_relations_fields
Merge remote-tracking branch 'origin/dev' into add_relations_fields
Add multiple choices relation field
Fix relation tests
Merge pull request #74 from spiral-project/add_relations_fields

Add relations fields