#1182 "open folder/file" etc. contextual menus

[Jean-Christophe Helary]

"open glossary folder" on the Glossary pane
"open TM folder" on the TM pane
"open TMX file" on a given match
"open source/target folder/file" on the Editor pane
"open segmentation preferences/file filters" on the Editor
"open TM preferences" on the TM pane
etc.