Add help and documentation on actual keyword to the editor menu * octave-qscintilla.cc(context_help_doc): new function for editor menu action; (get_global_textcursor_pos): new function for calculationg the cursor pos; (contextMenuEvent): uses get_global_textcursor_pos now, added context menu entry for documentation; (contextmenu_help,contextmenu_doc): slots for context menu; (contextmenu_help_doc): new common function used from context_help_doc and the context menu slots * octave-qscintilla.h: new functions context_help_doc, contextmenu_doc, contextmenu_help_doc, get_global_textcursor_pos * file-editor-tab.cc(context_help): new slot for editor menu action * file-editor-tab.h: new slot context_help * file-editor.cc(request_context_help,request_context_doc): new slots for help menu entries; (construct): new help menu with keyword help and documentation; (add_file_editor_tab): connect new signal fetab_context_help to the new slot context_help in file_editor_tab; (set_shortcuts): enable/disable new shortcuts when editor focus changes (check_actions): enable/disable new actions depending on existing tabs * file-editor.h: new signal fetab_context_help, new slots request_context_help and request_contest_doc, new help and doc actions