Use system default locale for date formatting in web UI

[qm3jp]

should resolve #3639

I used Intl.DateTimeFormat for the localized formatting, which has been widely on all major browsers since at least 2016.

Changes

• removed hard-coded date formatting
• added date formatting that uses the default system locale
• moved the docstring to be immediately before the date formatter function

Examples

locale	display
en-US
en-GB
de-DE
ja-JP-u-ca-japanese