New Uize.Test subclasses + Uize.Comm updates + other goodies

This pull request is highlighted by new `Uize.Test` subclasses aimed at providing helper methods for testing `Uize.Class` subclasses, `Uize.Widget` subclasses, and widget bindings.

There are also improvements to `Uize.Comm` and `Uize.Comm.Ajax` for error handling. The AJAX object would die before if an error occurred.

There are other miscellaneous fixes outlined in the commit logs.
I would assume not. The goal was parity with `Uize.Services.FileWshAdapter.Node` because that's what that code does.  I was seeing difference in functionality when switching between the two adapters. We discussed this way back when... What do you suggest?