Django-content-settings

* `cache_triggers` - module that adjusts
* setting value in code `content_settings.IS_OPEN = "-"`

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

* 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
* `result_validator`
* `PreviewValidator`, `PreviewValidationError`. More in [template types](template_types.mdcustom-validator).
* `SimpleExecNoCompile`.
* refactoring of template attributes. They all have prefix template now.
* `suffixes` attribute is a dict with function as value.
* `template_bultins` attrubute as a replacement for `allow_import`.