[Feature]: Add due date and priority colour coding

[thombruce]

Feature request

Due date should change colour dependent on status:

• Is distant (more than one week in future)
• Is soon (this week)
• Is overdue (date is in the past)

Priority should show one of four colours dependent on alphabetical position:

• A: High priority - something stark, like a red
• B: Medium priority - something mid, like an orange or amber
• C: Lowish priority - something calm, like a yellow or a green
• D-Z: Neutral - not officially supported, display in grey

Test the colours to ensure no conflicts or ambiguity with one another or other coloured elements (created/completed date, price, etc.)

Code of Conduct

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[thombruce]

Added: 40a9dede6988d9a3b18dbddef9b163c496e6be70