Django-siteprefs

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* import_prefs() regression fix.

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* IMPORTANT: added dependency - django-etc.
* IMPORTANT: manual autodiscover_siteprefs() call is not required after Django 1.7.
* Fixed KeyError in import_prefs (see 10)

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* IMPORTANT: added dependency - django-etc (fixed 13).

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* Fixed `manage` commands fail due to `autodiscover_siteprefs()` on Django 1.9.

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* Django 1.9 compatibility improvements.

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+ Djagno 1.7 ready.
+ Added Polish loco.