Drf-extra-fields

Rename package name to drf-extra-fields

- read_source parameter is added to PresentablePrimaryKeyField and PresentableSlugRelatedField.
- presentation_serializer accepts string path of the serializer class. For example: path.to.serializer.RepresentationSerializer
- Fix: https://github.com/Hipo/drf-extra-fields/issues/117
- Fix: https://github.com/Hipo/drf-extra-fields/issues/113

- Drop support for python 2.7
- Handle depracated FloatRangeField in django 3x
- Minimum django version to support is 2.2
- Minimum DRF version to support is 3.9.2

- Upgrade pillow

- Remove deprecated `ugettext_lazy`

- Handle invalid base64 inputs in Base64ImageField