[Requirements]Admin/Text and Video block

[DrFaust555]

As a user, I want to add text with a title and video to a StreetCode.

Acceptance Criteria

1. Admin is able to enter "Заголовок", limit is 50 symbols (uppercase and lowercase cyrillic and latin letters, numbers and special symbols).
2. Admin is able to enter "Основний текст". The limit is 25 000 symbols. The area for text is resizable.
3. Admin can apply basic formatting on text: bold and italic.
4. Admin is able to add a youtube.com link to "Відео", other links are not accepted.
5. Admin is able to request video preview via the "Попередній перегляд" button.
6. The "Відео" field is inactive until the Admin fills in the "Заголовок" field.
7. Admin is able to request a main text preview via the "Попередній перегляд тексту" button.
8. Admin is able to add text to the "Авторство" field. The text input field is prefilled with "Текст підготовлений спільно з". If this field remained unchanged - it will not be displayed for the user. Symbols limit is 200.