Consolidate various getValidValue widget methods

The code was very much not DRY, so has been consolidated into
WidgetModel (at least for now).
Improve javadoc for widget style constants
ChoiceWidget: add style constants
SwingChoiceWidget: add PRIORITY constant
Add Swing ChoiceWidget JRadioButton implementation

This respects the new ChoiceWidget styles to use radio buttons in a
horizontal or vertical orientation, rather than the default JComboBox.
ParameterTester: test the new ChoiceWidget styles
ModuleRunner: report Errors as well as Exceptions

Previously, we only caught RuntimeExceptions, so any Errors that were
thrown during module execution (or pre- or post-processing) were being
silently ignored.
InvalidCommand: apply some TLC so it works again

There were a few issues, but it now once again works as intended, with
two invalid parameters.

The "output" parameter was also an illegal shadow, so that one was
renamed to "out" to avoid confusion.

The "q" parameter was renamed to "x" since the latter actually *does*
shadow another private field from ParameterTester.

There were also minor improvements to the javadoc.

Most weirdly, the ParameterTester#cancel() method makes use of an
assumed-to-be-non-null LogService, which *will* be null in the case of
the InvalidCommand subclass because the ValidityPreprocessor fails out
the command before the ServicePreprocessor can populate the LogService.
To avoid the issue, we override the cancel() method to do nothing,
avoiding the NPE. Another way to avoid the issue would be to wrap the
ParameterTester#cancel() method's logging in 'if (log != null)' but that
would seem quite odd when studying that command, since it is seemingly
impossible for log to be null at that point in execution.
Merge branch 'radio-buttons'

This branch adds support for two new ChoiceWidget styles:
RADIO_BUTTON_HORIZONTAL_STYLE and RADIO_BUTTON_VERTICAL_STYLE.

These two styles use radio buttons instead of a dropdown list box to
render the choices of the multiple choice.

The branch also provides a Swing implementation of these widget styles,
SwingChoiceRadioWidget, which uses JRadioButtons.

Lastly, the branch fixes some minor bugs in the command framework
discovered during the course of implementing this feature, and makes
some minor improvements to the widget framework.