CPLayoutConstraint, CPLayoutContraintEngine, CPView support.
Partial CPContentSizeLayoutConstraint support.
nib2cib support (except symbolic weight, the 'standart' checkbox in IB').

cassowary-js-refactor: remove strict mode

Tests: CPLayoutConstraintTest is a test showing constraints manualy generated. Features Left/Top/With/Height and Width inequality. Click 'setup demo constraints' + 'Add Constraints' buttons.
       CPLayoutConstraintCibTest is a test for IB constraints.
Update cassowary submodule