FIXED: CPLayoutConstraint setConstant: or setProperty:

Change uuid when the constraint is already in the solver. This make
beleive to the Engine it’s a new constraint.
Autolayout Synchronized

This is the first version without WebWorker support. The previous
WebWorker enabled version is in the new branch  Autolayout-WebWorker.
Allows speed optimizations when communicating to the Engine (no son, no
web worker posting messages).
Also allows to better integrate the Constraint based layout system into
the current layout mechanism.
The default -layoutSubviews now updates out-of-date frames previously
changed by the engine.

Perf test (see Tests/AppKit/CPLayoutConstraintTest.j) shows we are
about the same seed as autosize. ±5% depending on the mask.
Added a cassowary/ dir to AppKit. This where lies cassowary.js and the
Engine wrapper.
Other changes: constraints (windowView <=> contentView) are now with a
required strength. Fixes a bug where the content view may not follow
the window.