refs #2433 Now thse classes accepts empty extensions, which is a bit dangerous in some cases.  This problem should be revisited in 3.2.

(cherry picked from commit 831d4e3bb794eaf28e150afa60ad16cd336677b4)

Conflicts:
	table-import-impl/src/main/java/org/cytoscape/tableimport/internal/io/WildCardCyFileFilter.java