Rename duration to date_range.

[aaronweeden]

WORK IN PROGRESS

Description

This PR renames the duration parameter to date_range and the get_durations() method to get_date_range_labels().

The duration parameter and get_durations() method will still work but are given deprecation warnings.

Motivation and Context

The goal is to have a parameter name that is more accurate and clear. "Duration" seems to imply a single number that represents the length of the time range.

Tests performed

Types of changes

• Refactoring / documentation update (non-breaking change which does not change functionality)
• 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 change)
• Release preparation

Checklist:

• CHANGELOG.md has been updated
• The milestone is set correctly on the pull request
• The appropriate labels have been added to the pull request
• Running the automated tests (see docs/developing.md) produces no errors
• Updates have been made to the xdmod-notebooks repository as necessary, and the notebooks all run successfully