Argument Parsing

- Obsoleted Command::exectute  'commandLine' argument.  It is worse
  than unnecessary, it is an uncategorized raw argument string, which
  is only really useful for the 'execute' command, which itself now
  calls Arguments::combine to reconstruct the command line string.

src/commands/Command.h

@@ -47,7 +47,7 @@ public:
   std::string description () const;
   bool read_only () const;
   bool displays_id () const;
-  virtual int execute (const std::string&, std::string&) = 0;
+  virtual int execute (std::string&) = 0;
 
 protected:
   std::string _keyword;