Upgrade to NetBeans Platform 9

Instant JChem has been upgraded to NetBeans Platform 9. Even though this upgrade is not primarily visible to the users, it ensures compatibility with future Java versions which allows for much smoother upgrades to the software.

By upgrade to NetBeans 9, IJC received support for visual themes. The preferred one can be selected in Tools → Options → Appearance → Look and Feel → Preferred look and feel.