Switch to native Intl.DateTimeFormat

[greentore]

Description

Removes dateformat dependency in favor of native Intl.DateTimeFormat object. 24-hour format is used by default with a settings switch to change it to 12-hour one.

Fixes #60

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

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[ajbura]

It is not clear why following changes want to remove the dateformat. closing in favor of #1739 for 24 hour clock