Override builtin navigation part identifiers

*Title: Override builtin navigation part identifiers

*Incentive:
Make it possible to override the builting navigation part
identifiers of modules and views.
If you are interested in moving a certain module or view
to another top menu you can use this without modifying
kernel code. 

*Documentation:
A new entry has been added to module.ini called ModuleOverrides.
In it the NavigationPart variable is found which controls
overrides for whole modules or views.

For instance to override a whole module you would add
NavigationPart[content]=ezsetupnavigationpart

or to override just a view you use the module name and the view name
NavigationPart[content/trash]=ezsetupnavigationpart