Official Django 3.0 support, Python 3.5+ Requirement

This is the first of two planned "triage" releases to update django-address

Release Notes:

• Django 3.0 compatibility
• Fix for None issue preventing normal use of the project. #90
• Fix for on_delete issue that impacted Django 2.2 and Django 3.0 differently.
• Update to project readme's stated requirements, project status and formatting. #102
• Update to setup.py to bump version and enforce updated requirements.
• Audit of and update to Example Site project interface and readme #105