2.2: Buttons Checkbox example
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**Primary Actor**: User

**Scope**: Ngx-bootstrap DEMO / BS version 3&4

**Goal**: Show user checkbox-like buttons example

Main success scenario:
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1. User opens Buttons demo page
2. User clicks on Checkbox sub-menu
3. User sees button-group, containing 3 clickable buttons named "Left", "Middle", and "Right", with the custom checkbox value field under it. 
4. By default, 1st button is inactive, 2nd - active and 3rd - inactive, and the text: "{"left": false, "middle": true, "right": false}" displayed in the checkbox value field above it.
5. User able to click on each button
6. When user clicks on the inactive button, it becomes active and the text in the checkbox value field next to the name of this button changed to "true"
7. When user clicks on the active button, it becomes inactive and the text in the checkbox value field next to the name of this button changed to "false"
8. User can make all buttons inactive and can make all buttons active

Variations:
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2*. User scrolls to Checkbox sub-menu