Put cursor:pointer on all interactive elements including buttons

[gabrielhl]

It makes everything easier and more consistent, even if there are intellectual and historical reasons why buttons don't do it. It also avoids this kind of situation:

It's a dc-btn-link. Looks like a link but has no pointer on hover.

some reference from other places
All buttons here in GH have cursor:pointer
Material Design Apps (Inbox, Google Drive) have cursor:pointer for all interactive elements
Bootstrap has cursor:pointer for all buttons
Foundation has cursor:pointer for all buttons