Add support for high resolution displays

At the moments all images in the navigation window (not the connection selection page) are pixelated on screens such as those with a Retina MacBook Pro.

Hopefully we can track higher resolution images of the existing artwork and can drag and drop them into the Xcode project.

Information can be found at https://developer.apple.com/resources/high-resolution/

[jeromelebel]

Not a priority, sorry.

[jeromelebel]

Should be fixed in 3.0. You can verify this issue, and close it.