Add Object.push, Object.unshift, and Object.concat methods
Fix shift vs unshift (unit tests to be updated)
Make PXObjectValueWrapper a subclass of PXObjectValue so we inherit all of object's methods

This will need a bit more cleaning up. Since this subclasses object, it should preserve property order. Also, we will need to decide if the wrapper is read-only, and if not, can the property wrappers be overwritten
Fix shift/unshift unit tests
Add optimizations for getSymbol, getProperty, and invocations of properties of a symbol

I was using the snapshot function as a test target. With these changes, that function dropped from 35 instructions down to 18.
Add optimizations for getting and invoking dotted properties.

This is a more general solution that covers getters and generalized dotted invocations. Admittedly, some of the optimization code in PXByteCodeBuilder (particularly addGetPropertyInstructionWithName) is a little ugly. We may want to consider a separate optimization pass that captures all of this logic elsewhere, thus making this step optional as well.
Fix comments