Add check for Model Checking tab in Preferences

In the Preferences, under Model Checking, there is the possibility to set the paths for the local tools to be used as backends. When the user selects a tool path, there is the need to click the Test button, to ensure that the tool meets the minimum version requirements.

Ideally, if the user doesn't do this check, it should not be possible to close the dialog and store the changes. Currently there in no such check.