Dataset selector dialog fix2

[xulman]

This PR adds:

• one extra commit left over from the previous PR (sorry for that!)

• N5Importer.runWithDialog() to import N5-ish containers always through the GUI dialog.

• the dialog can select/highlight an item at its opening

• the dialog enables/disables 'OK' button based on its availability

• the 'OK' was proposed to be renamed to 'Open in Imagej'

• the ENTER key was registered with this button

[xulman]

Example client code to operate this.