Fix media queries for Retina

[roborn]

Retina queries aren't working as expected.

• The media query for non-retina displays should use the max-resolution, instead of min-resolution;
• The media query for Retina diplays should use the min value on the prefixed device-pixel-ratio.

Also, i added the Opera prefix on both queries.

[Snugug]

Thank you. Here are some notes:

• Please place the dppx queries first; unlike properties where the standard should come last to ensure the cascade, when working with or MQs, the standard should come first as each or gets read independently. Because of this, the sooner the standard is found, the better.
• Please remove the Opera query. It was never really well supported by Opera and the dpi query will cover it.

[roborn]

Thanks for the feedback. Changes made :)

[Snugug]

Thanks. I'll take a look when I'm back at my computer