Use unicode Oscar slugs by default
Use unicode Oscar slugs by default

This commit enables OSCAR_SLUG_ALLOW_UNICODE. Without this, Oscar's
new (as of 2.0) internal slugification will generate wildly long
slugs for unicode titles (like cyrillic ones). These long titles will
exceed the slug column width (255).

Unfortunately, Oscar does not use AutoSlugField, so it doesn't simply
cut off the slug or add a suffix on duplicates. Instead, it'll throw
an exception if you give it a unicode title of sufficient length.

The slugs that Oscar generates are only used internally, or not at
all, I believe. Between Open edX services, we mostly use the SKU.
So this should be a completely transparent change.

DISCO-1616

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