Django-map-widgets

- Removed `six` package usages. (117)
- Added a new general widget setting in order to specify Google JS libraries. (119)
- Implemented some improvements for the demo project.

- Implemented a new demo project with Django 2.x.
- Fixed Django Admin jQuery conflicts 100
- Fixed a new widget JS instance initialising issue for Django Admin Inlines 84
- Updated TravisCI conf(added `python 3.8` settings)

> - Fixed python `six` module import issue.
> - Fixed PostGIS setup errors in CI pipeline.
> - Added Estonian language support.

- The document updated.
- Fixed swapped coordinates bug

- Fixed swapped coordinates bug 60

> - Fixed Python 3.6, Django 2.x compatible issues.
> - Fixed SRID format converter issues.
> - Removed `pyproj` package dependency.
> - Various development infrastructure updates. (Docker, Fabric files etc.)
> - Point map widget JS objects associated to the map HTML elements with jQuey `$.data` method.
> - Passing Google Place AutoComplete full response object to jQuery triggers.