Better display of Date/Time in Explorer

[HartS]

From looking at the https://explorer.cardano.org/en.html , there's absolutely no indication to users what time zone is being used for date/time display.

For example, if I look at the "Started at" column , for epoch 258 (the current epoch at the time of filing this), I see 2021/04/05 21:45:46

What does this translate to in my time zone? Is it already my time zone? Another time zone?

Looking at the graphQL updates in the network panel, or the source code I can determine that this is in fact UTC.

UTC isn't immediately as helpful to users, and it would be fairly trivial to translate to their local time zone. And if UTC is preferred, suffixing the date string with Z (so 2021/04/05 21:45:46Z instead of 2021/04/05 21:45:46) is the more accurate way to display this... users have some indication what time zone the date is for. More technical users can paste this directly into their console:

new Date("2021/04/05 21:45:46Z")
Mon Apr 05 2021 14:45:46 GMT-0700 (Pacific Daylight Time)

less technical users can google What does "Z" in a date mean and immediately get a useful answer .

I'd be happy to make a PR to implement one of these solutions for all places dates are displayed. Though I just noticed there's also no CONTRIBUTING.md or any contributor guidelines specific to cardano-explorer-app I've been able to find, so let me know what needs to be done here.