Change production English locale (fixes #2794)

[paulbert]

Trying out en-GB, could use en-EU instead.

Change is so the app uses 24 hour time and euro style date formats.

[paulbert]

Doing my own tests, it looks like this causes problems with the datepicker forms where the date and month switch after typing. For example typing 5/12/2019 will immediately change to 12/5/2019 when inputting the form or moving to another field.

I think we need to incorporate Moment.js for this to work since the default DataAdapter only supports en-US (see https://material.angular.io/components/datepicker/overview#choosing-a-date-implementation-and-date-format-settings)