Fixed: CPWindow -layout. See intrinsicContentSizeTest.
Fixed wrong contentView size after resize: was setting size twice, one via casso variables solving, two via _windowView subviews autosizing.
Skip casso update for contentView for now. We need to disable autosizing for _windowView subviews by converting masks into constraints and re-enable casso-driven contentView
frame later.

Fixed a silly bug introduced in Window -setFrameSize: when autosizing. Back to normal with ojtest -translateIntoConstraints ok.

CPLayoutConstraintTest: changing a constraint property now marks the view needsUpdateConstraints and correctly updates constraints in the solver at the next resize.
                        Popover explaining the priority level, like in IB.
Edit vars with priority: currently medium 1000 for everyone (was strong 1).