Make preferences pane correctly resize

[rschiang]

After some through study of the issue, I could track down the cause of collapsing preferences pane should be related to autoresizeSubviews. Interface Builder would warn about ambiguous constraints and AutoLayout stuff, but they are mostly red herrings (unless we ditch OS X 10.8 and switch to NSStackView, eliminating most of the painstaking constraints).

This should fix #1103.

[rschiang]

This PR changes two things:

• Set autoresizeSubviews="YES" (should be the default according to official doc).
• Fix incorrect top padding value from 25 to 11.

I'm aware that autoresizeSubviews="NO" has been sitting in the codebase for a while. My judgement was that previously sloppy NSBox implementation ignored the property value, as problems only started emerging in last year.

The padding change is to fix the consistency of the top and bottom margin. I don't have a 10.8 system around, so I'm not sure if it breaks in the earlier version. Looks good on 10.14 though.

[FranklinYu]

Verified the fix with Xcode. LGRM.