Constant prop add (#849)

* add FoldADD to const prop, add yosys miter tests

* add option for verilog compiler without optimizations

* rename FoldLogicalOp to FoldCommutativeOp

* add GetNamespace and RenameModules, GetNamespace stores namespace as a ModuleNamespaceAnnotation

* add constant propagation for Tail DoPrims

* add scaladocs for MinimumLowFirrtlOptimization and yosysExpectFalure/Success, add constant propagation for Head DoPrim

* add legalize pass to MinimumLowFirrtlOptimizations, use constPropBitExtract in legalize pass