<issue_start><issue_comment>Title: Add countdown for Referenda end/delay
username_0: We're currently showing block number. It'd be much better with days/hours based on the network constants.

We should build a `countdown` component that will fetch the constants and
- show the remaining time (with accurate to the minute) if in the future.
- it should show the block timestamp if in the past I think that's possible to get.
- on mouse over it should show the block number.
<issue_comment>username_1: Just to clarify, do you mean the network's current block number or the block number of the referendum's end? For now I put these three in there:
<img width="509" alt="Screenshot 2020-04-19 at 17 49 59" src="https://user-images.githubusercontent.com/7072141/79692728-0bd56c00-8267-11ea-8662-58b0240c1a1f.png">
<issue_comment>username_0: The 3 info is too much I think. When there is a block number, replace it with countdown and have this block number as pop-up.
<issue_comment>username_1: Okay, so out of the three currently in the popup only the referendum's end block number?
<issue_comment>username_0: yup,  if you're replacing the the "end block", but if we're talking about the delay, then it'll be the enactment block, which is end+delay.<issue_closed>
<issue_comment>username_0: done in #683