[Scenario] Add checks to result of CSV file dialog

Add checks around the file chooser used
to pick a target CSV file for export
during the Export CSV action.
[Scenario] Move CSV file chooser into own class
[Scenario] Show confirm dialog if export file exists

Prompt the user with a confirmation dialog
when attempting to export a CSV to a file
which already exists, in order to avoid
destroying existing data.

Note that JOptionPane is used instead of
WindowManager here; the latter is generally
preferred to avoid introducing Swing
dependencies around dialogs, but we
already have a Swing dependency here since
the dialog is being launched from a
JFileChooser.
[Scenario] Use showSaveDialog method for CSVFileChooser

Use the showSaveDialog method of CSVFileChooser
to clarify in the code that the file is being
saved, and check for this before prompting to
confirm. This clarifies code and simplifies any
future implementation of an Import CSV feature
that might reuse the same dialog.
[Scenario] Remove sleep used to verify CSVExportWorker

Invocation of Thread.sleep had been used to
ensure there was time for Progress Monitor
to appear.
[Scenario] Explicitly include tags in CSV export