Added Greek Language and updated source_en.ts
Add support for Greek Language.
All strings are translated with latest master commits.
Very small corrections need to be made (like full word for shortcut etc), but I would like take time to see in long practice how it's go.
SPECIAL NOTE ONLY FOR source_en.ts file: After I updated the source_en.ts with pylupdate5 for all python files, I have did search and replace with text editor, filename='../ to filename='../.. so to point to python files like it was inside el_GR directory. Also I didn't run update for resources.