Refactor show_editable_model. Add show_editable_model_icon that adds an icon attached to model editing.
CSS edit for show_editable_model_icon
Fix js Style
Refactor and rename show_editable_model. Add other render_model* templatetags.
Update tests. Add tests for new render_model templatetags
Coverage improvement
Fix url
Cleanup
Add getter & setter for translatable_content in CMSPlugin
Typo
Added tests for get/set_translatable_content
cosmetic changes for @piquadrat
Update documentation for render_model templatetags
wording changes in comments
Removed uneccessary utf-8 encode
Removed get_plugin_instance in getter/setter

If you're not calling these methods from the instance you're likely to use the CMSPlugin's methods instead of the ones of your plugin
Use custom (overridable) icons for render_model_icon and render_model_add
fixed logic
Code cleanup
Use a transparent placeholder and CSS background for render_model_icon and _add.