Allow to enable extra apps in settings

fix #52

README.md

@@ -250,6 +250,7 @@ Settings
 
 List of available settings in your `settings_local.py` file.
 
+- `EXTRA_INSTALLED_APPS`: See *Customizing app list*
 - `MEMBER_MEMBERSHIP_INFO_URL`: Link to a page with information on how to become a member or pay the membership fee
 
 More information

coin/settings.py

@@ -167,6 +167,8 @@ INSTALLED_APPS = (
     'simple_dsl'
 )
 
+EXTRA_INSTALLED_APPS = tuple()
+
 # A sample logging configuration. The only tangible logging
 # performed by this configuration is to send an email to
 # the site admins on every HTTP 500 error when DEBUG=False.
@@ -254,3 +256,4 @@ except ImportError:
     pass
 
 TEMPLATE_DIRS = EXTRA_TEMPLATE_DIRS + TEMPLATE_DIRS
+INSTALLED_APPS = INSTALLED_APPS + EXTRA_INSTALLED_APPS