Create top-level options category "Gephi" and hide irrelevant Netbeans option panels

[mbastian]

We leverage the built-in Options system in Netbeans Platform to have options settings panels. We would like to facilitate panel creations, including in Plugins.

Definition of done

• Removal of unnecessary Netbeans panels (Keymaps, Misc/Janitor, Misc/FilesAssociations)
• Creation of a generic "Gephi" top category
• Removal of the "Visualisation" top category and wrap into "Gephi"

As we don't have a lot of options panels I think it makes sense to wrap all of them under the Gephi category for now. Easier to find and maintain.

This is how a plugin could add its own panel under "Gephi":

@OptionsPanelController.SubRegistration(location = "Gephi",
    displayName = "#GephiOption_DisplayName_MyPlugin",
    keywords = "#GephiOption_Keywords_MyPlugin",
    keywordsCategory = "Gephi/MyPlugin",
    position = 600)