Moving Form into separate namespace.

In preparation for the upcoming Form rewrite.
Big cleanup of Html class and test.
Html::options() throws \Exception on bad args.
Adding the beginnings of a FormRow class.
Adding error message to FormRow.
Rendering of label, input and error in FormRow.
Adding FormRow getValue() and setValue().
Adding getType() and setType() to FormRow.
Adding Html::label().
Stricter comparisons in HtmlTest.
Testing changing the type of FormRow.
Form rewrite to use FormRow.
Creating sensible labels in FormRow automatically.

Thanks to Daniel St Jules' excellent Stringy library.
Docs and tests for Form label() and error().
Html - removing ids from labels, adding to inputs.
Using Html::label in tests.
Adding Form submit() with automatic value.
Adding Form hidden() plus improving FormTest.
FormTest cleanup.
Adding Form getFields().