Debugger: Refactor + resolve TODO.

- Introduce interface class ValueFormatter. This one takes on the
responsibilities of formatting a value into a string, which were
previously embedded within the various TableCellValueRenderer
subclasses.
- Add implementing subclasses for the various value types.
- Introduce TableCellValueRenderer subclass TableCellFormattedValueRenderer.
This is a simple TableCellValueRenderer implementation for the simple case
of a renderer that does nothing more than use a formatter to present a
string version of its corresponding Value. Since this describes all existing
renderers, this renders them obsolete.
- Refactor the respective ValueHandler subclasses to make use of the formatters
and new rendererer subclass.

Debugger: Refactor + resolve TODO.

- Introduce interface class ValueFormatter. This one takes on the
responsibilities of formatting a value into a string, which were
previously embedded within the various TableCellValueRenderer
subclasses.
- Add implementing subclasses for the various value types.
- Introduce TableCellValueRenderer subclass TableCellFormattedValueRenderer.
This is a simple TableCellValueRenderer implementation for the simple case
of a renderer that does nothing more than use a formatter to present a
string version of its corresponding Value. Since this describes all existing
renderers, this renders them obsolete.
- Refactor the respective ValueHandler subclasses to make use of the formatters
and new rendererer subclass.