Wagtail-fedit

* Add docstrings
* Add tests
* Refactors for uniformity
* Fix docstrings for hook definitions

* Fixed exception when value returned from modelfield is None.
* Add example image in README

* Big updates to README.md
* Add docstrings in hooks.py
* More uniform permission checks in template tags.
* Github actions WF for testing
* Fixes to javascript; now including `_editor_js.html`

Changes
* Change `{% fedit_field %}` tag parameters. **Check the readme!**
* Fade out the old element and then fade the new replacement in.
* Add tests for when object is locked
* Refactor urls.py to reduce code duplication
* Add admin action menu item for snippets and pages
* Fix admin styles for locked objects

Tested, production ready Frontend Editing for your Wagtail website.