Django-content-settings

* `UserTagSetting.tag` is now charfield, so it works correctly with MySQL
* Django Admin UI updated, and more space dedicated to help text

* using migrate module you can add content settings change into migration

* Make sure all types can work with empty values (when those are not required)
* change verification order
* new setting `CONTENT_SETTINGS_VALIDATE_DEFAULT_VALUE` - validates not only DB values but also default values

* Move split by first line into a separate repo. [dcs-split-by-first-line](https://github.com/oduvan/dcs-split-by-first-line)

* `DjangoTemplateNoArgsHTML` and change `DjangoTemplateHTML`
* `ProcessorsMixin` and `GiveProcessorsMixin` new mixins. More in [types](types.mdmixins-source)
* new doc about [template types](template_types.md)
* `result_validator`
* `PreviewValidator`, `PreviewValidationError`. More in [template types](template_types.mdcustom-validator).
* `SimpleExecNoCompile`. More in [template types](template_types.mdsimpleexecnocompilesystemexec-staticdatamixin-simpletext).
* refactoring of template attributes. They all have prefix template now. More in [template types](template_types.md).
* `suffixes` attribute is a dict with function as value.
* `template_bultins` attrubute as a replacement for `allow_import`. More in [template types](template_types.md).

* new [settings](settings.md) - `CONTENT_SETTINGS_CHECK_UPDATE_CELERY` and `CONTENT_SETTINGS_CHECK_UPDATE_HUEY`
* fix `widgets_attr`