Updates to plugin and dependency versions

Added `-c` Clear Cache command line optino

Updated date in LICENSE file
Added a holiday test, but couldn't really get it to work - it's commented out
Added the `-c` command to the README and the Help

Fixed snap bug with java prefs

Fixed bug where holidays wouldn't show up in single months

Corrected display error if the holiday's coudn't be retrieved
Added another test for single month holidays

Add holiday list for month only display

Added maven enforcer plugin requiring mvn >= v3.2.5
Show holidays for the active month in the month only display
Moves display holidays code to the holiay class
Display locale when in debug mode (near the command line switch output)
Tweaked month validation when both month & year are given
Added another calendar output test (for Nov 2026)

Added more error handling to holiday function

Remove unneeded parameter from Calendar.PrintYear

Dependency updates. Updated screenshot.

Also cleaned up the code a small bit, added comments, etc.

Implemented jCommander replacing GetOpt

This includes a test class to ensure it's
working correctly

Updates to latest version of dependencies