Custom navigation part identifiers

*Title: Custom navigation part identifiers

*Incentive:
Make it possible for extensions to create custom
navigation part identifiers for their own modules.
This can be used in conjunction with the new topmenu
system to create custom tabs in the admin interface.

*Documentation:
The navigiation part identifiers have been moved from
PHP code in eZNavigationPart and into the INI file
menu.ini.

The list is defined by an associative array in the
NavigationPart group in a variable called Parts.

To create your own part simply add a new entry.

Example:
Part[ezcustomnavigationpart]=Custom

Note: Make sure your identifier is unique, identifiers starting
      with ez is reserved for eZ Systems.

Translations:

The text in the INI file will not be translatable unless you create
some dummy PHP code somewhere.
Create a new PHP file in your extension or add a dummy function to
one of your classes and add

ezi18n( 'kernel/navigationpart', 'Custom navigation', 'Navigation part' );

Then run ezlupdate with your extension. You should then find the string
in the translation file(s).