Allow override which voip_modules load per user config like apps.

Just need array list of voip modules to load in users voip app config. Example from user's db doc:
...
   "apps": {
       "voip": {
           "id": "voip",
           "label": "Hosted PBX",
           "icon": "device",
           "desc": "Manage vmboxes, callflows ...",
           "api_url": "http://kazoo.example.com:8000/v1",
           "default": false,
           "modules": [ "account", "bulk", "media", "device", "callflow", "conference", "groups", "user", "phone", "vmbox", "menu", "registration", "resource", "featurecode", "cdr", "queue", "directory" ]
       },
   .....
},
...