Enforce unique AuthServicesInfo (#618)

Alter user field to OneToOneField
Migration to enforce uniqueness pre-change
Migration to ensure all users have an AuthServicesInfo
Receiver to automatically create one upon user creation
Replace AuthServicesInfo.get_or_create with get
Prevent deletion of AuthServicesInfo from admin site
Remove add and delete permissions from model.

Get character names in chunks on corpstats update to prevent HTTP400 when requesting >350(ish) names

Include corpstats docs.
Update settings docs.

services/managers/eve_api_manager.py

@@ -325,7 +325,7 @@ class EveApiManager:
             raise e
         except (requests.exceptions.RequestExeception, HTTPError, URLError) as e:
             raise EveApiManager.ApiServerUnreachableError(e)
-        auth, c = AuthServicesInfo.objects.get_or_create(user=user)
+        auth = AuthServicesInfo.objects.get(user=user)
         states = [auth.state]
         from authentication.tasks import determine_membership_by_character  # circular import issue
         chars = info['characters']