Add display utility classes

[krystynek]

• d-block
• d-inline-block
• d-flex
• • flex-row
• • flex-row-reverse
• • flex-column
• • flex-column-reverse

[aditya28sarin]

Can you assign me on this issue?

[aditya28sarin]

Hey, where do I have to add these utility classes? Like in the sass file? and what content to fill inside?