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[rowanh22]

Closes #101

Now blank maps are supported, colour picker is a colour palette, and fixed a bug regarding saving maps not working. Minor styling changes regarding mouse pointer and removed unused toolbar icons.

• [ ] Change in CHANGELOG.md described (if applicable)
• [ ] Tests created for changes (if applicable)
• [ ] Manually tested changed features in running JabRef (always required)
• [ ] Screenshots added in PR description (for UI changes)
• [ ] Checked documentation: Is the information available and up to date? If not created an issue at https://github.com/JabRef/user-documentation/issues or, even better, submitted a pull request to the documentation repository.