Timezones: Seperate display timezone and consistency update

[ssddanbrown]

For #4786

Adds a new option to define the display time-zone separately from the storage/database time-zone.

Todo

• Update existing time displays in-app to new use util class.

Doc Notes

• Update notice: Advise existence of new option.
• Update docs page about the timezone option.
  • Document the new option.
  • Update wording/detail for the existing timezone option.
  • Advise use of UTC for APP_TIMEZONE.
  • Mention possible shifts when changing APP_TIMEZONE value.