enable theming via external "theme" directory

This is compatible with the existing theming for LMS.

notifier/settings.py

@@ -2,6 +2,7 @@ from datetime import timedelta
 import logging
 import os
 import platform
+from theming import enable_theme
 
 DATABASES = {
     'default': {
@@ -86,6 +87,11 @@ LOG_LEVEL = os.getenv('LOG_LEVEL', 'INFO')
 # datadog
 DATADOG_API_KEY = os.getenv('DATADOG_API_KEY')
 
+# Theme
+THEME_NAME = os.getenv('THEME_NAME', None)
+if THEME_NAME is not None:
+    enable_theme(THEME_NAME)
+
 # celery
 import djcelery
 djcelery.setup_loader()

notifier/theming.py

+def enable_theme(theme_name):
+    """
+    Enable the settings for a custom theme, whose files should be stored
+    in ENV_ROOT/themes/THEME_NAME (e.g., edx_all/themes/stanford).
+
+    The THEME_NAME setting should be configured separately since it can't
+    be set here (this function closes too early). An idiom for doing this
+    is:
+        THEME_NAME = os.getenv('THEME_NAME', None)
+        enable_theme(THEME_NAME)
+    """
+    # Calculate the location of the theme's files
+    theme_root = ENV_ROOT + "/themes/" + theme_name
+
+    # Include the theme's templates in the template search paths
+    try:
+        TEMPLATE_DIRS
+    except NameError:
+        TEMPLATE_DIRS = [
+                os.path.join(PROJECT_ROOT, "templates/"),
+                ]
+    TEMPLATE_DIRS.insert(0, theme_root + "templates/")
+
+    # Namespace the theme's static files to 'themes/<theme_name>' to
+    # avoid collisions with default edX static files
+    try:
+        STATICFILES_DIRS
+    except NameError:
+        STATICFILES_DIRS = [
+                os.path.join(PROJECT_ROOT, "static/"),
+                ]
+    STATICFILES_DIRS.insert(0, ("themes/%s" % theme_name, theme_root + "/static"))
+
+