ProductVariationAdmin is too wide.

[ryneeverett]

This inline makes the width of the entire Product admin page really wide, which forces users of smaller laptops to do horizontal scrolling. I'm not the first to notice this:

• https://groups.google.com/d/msg/mezzanine-users/l3sOM8Lnop4/78hz_p46bRkJ
• https://groups.google.com/d/msg/mezzanine-users/7hfuZYqhqoI/fgIdW06gRyMJ

Seems like the obvious solution is to switch it to a StackedInline. Does anyone prefer TabularInline? If so we could make the admin base class a setting.

[stephenmcd]

I think having all the variations laid out like a table/spreadsheet is super useful for someone managing the products, they can easily scan over one of the columns to see all the values.

Looks like it's the sale start/end dates are the columns that are blowing out - maybe we can do something with those via CSS or some custom HTML to keep them slimmer.