[krbdev.mit.edu #5724] NIM: FEATURE: APP: Default Identity Context Menu

[Jeffrey Altman via RT]

There should be another menu item on the NIM tray icon context menu
that allows switching the default identity.  Something like "Set
default identity-> list of identities".  Similar to how the delete
and renew options work.   All identities should be selectable regardless 
of whether or not credentials are present.