[Paintroid-515] Use Paintroid keys for translations

[Knist1704]

This pull request refactores the app to use localization keys similar to the ones used in the Paintroid-Kotlin project.
Jira Link

New Features and Enhancements

• Localization with Paintroid-Kotlin keys in main paintroid and colorpicker package

Refactorings and Bug Fixes

• Existing hardcoded strings are now localized
• Edited existing test cases to be more in line with the Paintroid-Kotlin project
• Added keys for the "project" and other new features of the flutter version
• Unused crowdin files delete

Checklist

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