WPSC Theme CSS cleaning.

Minor clean-up to the theme css files.
- Extra whitespaces and old commented out code removed.
- Typo corrected: .default_ * to: .single_product_display .wpsc_variation_forms and .single_product_display .wpsc_quantity_update (are these needed or redundant?).

It might be neat to include a minified version for serving on live sites and add the '-dev' suffix to this current full-fat css for those wanting a hackable version (as per WP core). Counter-argument is that this may create confusion for new adopters, and pro-users do this anyway(?). In general, all fairly static CSS could be minified for WPEC where User hacking is not anticipated; it may be worth auditing.