Make document language choices a configurable list. Issue #137.

To override the default list of 600+ languages add a configuration entry to your settings/local.py like so:
DOCUMENTS_LANGUAGE_CHOICES = [('eng', 'English'), ('deu', 'German')]

to make the list translatable import ugettext_lazy and enclose the language name with _():

from django.utils.translation import ugettext_lazy as _
DOCUMENTS_LANGUAGE_CHOICES = [('eng', _('English')), ('deu', _('German'))]

mayan/apps/documents/models.py

@@ -32,12 +32,11 @@ from mimetype.api import get_mimetype
 
 from .events import event_document_create
 from .exceptions import NewDocumentVersionNotAllowed
-from .literals import LANGUAGE_CHOICES
 from .managers import (DocumentManager, DocumentPageTransformationManager,
                        DocumentTypeManager, RecentDocumentManager)
 from .runtime import storage_backend
-from .settings import (CACHE_PATH, DISPLAY_SIZE, LANGUAGE, ZOOM_MAX_LEVEL,
-                       ZOOM_MIN_LEVEL)
+from .settings import (CACHE_PATH, DISPLAY_SIZE, LANGUAGE, LANGUAGE_CHOICES,
+                       ZOOM_MAX_LEVEL, ZOOM_MIN_LEVEL)
 from .signals import post_version_upload, post_document_type_change
 
 HASH_FUNCTION = lambda x: hashlib.sha256(x).hexdigest()  # document image cache name hash function