* Split `helpers.py` into separate `url.py`, `permission.py` and `button.py`, dedicated to those separate concerns and update the docs accordingly
* Move `ThumbnailMixin` out to `mixins.py` and update documentation accordingly
* Ad #NOQA to import lines to hush pep errors
* Alphabetise helper import order
* - Delete `helpers/helpers.py`
- wagtal -> wagtail in docs
- Remove imports at the top of options.py and views.py that result in ImportError when those apps aren’t installed
- Alter ThumbnailMixin and InspectView to use the `wagtail.wagtailimages.shortcuts.get_rendition_or_not_found()` method to render images, which handles missing image source files gracefully, and reduces code duplication.
- Simplify `get_field_display_value()` by not limiting image and document rendering to ForeignKey fields. It should work consistently for property methods or other attributes too.
* `result_row_display` adds a `data-object_pk` attribute to each row, to make items easier to identify with JS
* Adds `get_extra_attrs_for_row()` method to `ModelAdmin`, to give developers a way of adding further attributes to the `<tr>` element
Andy Babic