Merge pull request #507 from OpenTechFund/bugfix/allow-presigned-urls-for-private-files

opentech/apply/funds/migrations/0042_update_json_encoder.py

opentech/apply/funds/models/mixins.py

opentech/apply/funds/models/submissions.py

opentech/apply/funds/tests/test_models.py

opentech/apply/stream_forms/blocks.py

opentech/apply/stream_forms/fields.py

opentech/apply/stream_forms/files.py

...eam_forms/templates/stream_forms/includes/file_field.html

...tream_forms/templates/stream_forms/render_file_field.html

...forms/templates/stream_forms/render_multi_file_field.html

opentech/apply/stream_forms/testing/factories.py

opentech/settings/base.py

opentech/storage_backends.py