revert on invalid assignment
tests for assertions on complex object
test for multiple assertions on a single variable
added tests for trigger mechanism
added TriggerSolver
added tests for layer activation
added simple  layer activation implementation
added postponeEnabling flag to cassowary
added tests for scoped constraints
added first implementation of scoped constraint
added postponeEnabling flag to DeltaBlue
added tests for scoped assertions and triggers
scoped assertions and triggers