Jump to Line

Added a "Jump to Line" menu action to the Edit Menu (with the standard Ctrl+G keyboard shortcut) in order to access "jump to line" functionality that already existed.  Also cleaned up the actions file and added a description to improve maintainability, legibility and documentation.

The action added to the actions.py file is:

{
  "shortcut": "Jump",
  "action": {'text': translations.TR_JUMP_TO_LINE,
                 'section': (translations.TR_MENU_EDIT, None),
                 'weight': 240},
   "connect": "editor_get_jump_to_line_number"
},