Django-content-settings

* Fixing a lot of bugs with admin of content settings. Such as preivew, search, tags filters and cetera
* fixing dynamic work with local changes in content settings
* fix help text for user defined types
* if variable constant or removed from code - admin is not allowed to see it in django admin
* new type `DjangoModelTemplateHTML`
* fix issue with \r\n in tags field for user defined types
* remove attribute `empty_is_none`, we have `EmptyNoneMixin` mixin instead
* `validators` can be tuple and list now
* `EachMixin` now works only with expected types.
* new class for `EachMixin` - `each.Values` - convers all values in the dict
* fixing bugs with lazy object
* for `CallToPythonMixin`, `preview_validators` and `admin_preview_call` are removed. Now, all of the validators, that are instance of `call_validator` will be shows in preview and settings call will be always shown if more than one validators are for preview
* the change above requires massive refactoring for preview of template/call types
* if `SimpleCallTemplate` doesn't have a required arguments and doesn't have validators - the system uses one validator `call_validator()`
* `DjangoTemplateHTML(HTMLMixin, DjangoTemplate)` -> `DjangoTemplateHTML(HTMLMixin, DjangoTemplateNoArgs)`

* `SplitByFirstLine.split_key_validator_failed`
* fix preview for `each.Keys`

* `EachMixin`
* `HTMLMixin` and `DjangoTemplateHTML`
* showing type name(s) in admin panel
* migrate can also show "adjust" in case of changing tags or/and help
* yet another admin preview function refactoring.
* fix quoting in text/python preview

* Default preview for Exec and Eval is Python
* SimpleBool more possible input options
* help_format for SplitTranslation
* test covarage: 95%

* __content generated tags__ - tags that can be generated not based on the given tags, but based on the given value.
* `CONTENT_SETTINGS_TAGS` - a list of functions that can generate tags for variable based on value
* `view_permission` and `view_history_permission`
* `SimplePassword`
* `json_view_value` returns string

* `caching.get_raw_value` - new function
* `context_manager.process_set` - correct work with str, list and other iterable (those will be converted to set)
* prevent resetting value if only help of tags were updated. The value will be reset to default only in case of version update