Lola/feature/57 look and feel

[lolagarden]

Implements some look and feel changes (#57) regarding icons and favouriting/read functionality. Also #106 which was the unlink

• [x] Change in CHANGELOG.md described (if applicable)
• [ ] Tests created for changes (if applicable)
• [x] Manually tested changed features in running JabRef (always required)
• [x] Screenshots added in PR description (for UI changes)
• [x] 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.