Allow users to choose their own date & time formats

[fiveoaksmn]

Is your feature request related to a problem? Please describe.
Right now the date format and time format is selected in system settings and is globally applied. Certain countries have different preferred formats. And even in the same country, I have found people with different backgrounds (scientist for example) prefer different formats.

Number formats have the same problem too so if it's easier to do them all at once, I would propose that but for me personally, the date/time format is the bigger need.

Describe the solution you'd like
A new doctype that the allows the admin of the site to specify different date and time formats (maybe you create two doctypes - one for date format, one for time. Or maybe put them all under one. Either option I think is acceptable). Pre-populate it with the current formats that are found in system settings. Allow specification of which one is considered the default. On the user account, link to this table of what date and time format is to be used. When a new user account is created, it takes whatever is set as he default. Allow both the admin access to change for the user as well as the user themselves in the "My Settings" view.

Describe alternatives you've considered
There really all no alternatives right now.

Additional context
I don't have anything additional at this time.