Cmsplugin-blocks

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* Added ``establishment_opening`` model/form/plugin/template;
* Cleaned template from private integration to basic HTML.

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* Renamed Diptych ``background`` field to ``image``;
* Use Diptych ``alignment`` field value in its template.

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* Removed useless basic models and forms from development.

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* First commit for banner, slider and diptych blocks.