Don't crash when a nomcom is partially set up.

[rjsparks]

Right now, if a nomcom group is created, and the associated NomCom object is not, anyone with a role in the nomcom group cannot use the datatracker - the construction of the menu crashes.

The places that crash need to be protected against this misconfiguration (especially while the configuration of the Group and NomCom objects are done manually).

See also #3289

[jennifer-richards]

There's a template filter, active_nomcoms that currently returns all the groups of type nomcom for which a user has a role. The template then looks backwards across the foreign key relationship to find the NomCom object. This is backwards - the filter should return NomCom instances. This avoids having to deal with the possibility that the Group does not have a NomCom.

Patch shortly.