Customisable date/time formatting (including iso 8601)

May I suggest to use the iso way for formatting dates and times?

https://xkcd.com/1179/

Currently, e.g. the "last used" value for the devices (settings dialogue) looks like this:
```
myip @ 2/1/2017, 12:10:34 AM
```
... which is confusing for non-american non-12h clock users. iso-like formatted it would look like this:
```
myip @ 2017-02-01 00:10:34
```
(which is also the way it sorts naturally).