Add an "are you sure" popup window when you click block checkmark

[RynTurtle]

I just accidentally unfollowed someone by clicking the checkbox when having the viewercard open, losing our followage, I suggest having a popup window with an "are you sure" message would be perfect to prevent any stupid missclicks and ensure that it doesnt happen to anyone else.

[jupjohn]

If this change gets implemented and a dialog pops up on block I'd suggest changing the block action from a check box to a button. If we want to indicate state (blocked or not), then that could probably be indicated in the summary text (perhaps next to the username in brackets)

[Mm2PL]

What if we disallowed clicking the block checkbox if the target is followed. We can still check that iirc. Usually users don't want to block someone who they follow.