CLI2: Simplify context determination

Simlifies by offloading portion of the logic into the singleton Context
class (which has nothing to do with the task context per se, just a
implementation singleton).

src/Context.h

@@ -57,6 +57,8 @@ public:
   int getWidth ();                     // determine terminal width
   int getHeight ();                    // determine terminal height
 
+  std::string getTaskContext (const std::string&, bool fallback=true);
+
   const std::vector <std::string> getColumns () const;
   void getLimits (int&, int&);