Admin/Text and Video block


### Acceptance Criteria

1. Admin is able to enter "Заголовок", limit is 50 symbols
2. Admin is able to enter "Основний текст". Limit is 15 000 symbols. The area for text is resizable.
3. Admin can apply basic formatting on text: bold and italic.
4. Admin is able to add youtube.com link to "Відео", other links are not accepted
5. Admin is able to request video preview via the button
6. Admin is able to request a main text preview via "Попередній перегляд тексту" button.
7. Admin is able to add text to "Авторство" field. Text input field is prefilled with "Текст підготовлений спільно з". If this field remained unchanged - it will not be displayed for user. Symbols limit is 200.


### Acceptance Criteria for dictionary functionality
1. Admin is able to select a text and link it with an existing element from the dictionary or create a new one, so a description will be displayed when user will be hovering a cursor over a linked text.
2. Admin is able to unlink previously linked text
3. Admin is able to add a new item to the dictionary via a button, a modal window should be opened with mandatory fields for the name and explanation for a new item.
4. Limits for text fields:
Name - 50
Description - 500