fix: Prevents CTRL+P from being masked by a given accelerator defined in FXML (#553)

[Oliver-Loeffler]

This quick fix will prevent CTRL+P from being blocked by a accelerator defined in an FXML. CTRL+P is used to display the preview window and it works with some FXMLs, not with others.

A clean solution to this requires lot more work. With the current way the Scene Builder works, the problem can occurr with any other accelerator defined in Scene Builder.

Issue

Fixes #553

Progress

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