Allow sorting find zone groups by mean time per call.

server/TracyView.hpp

@@ -290,7 +290,7 @@ private:
     struct FindZone {
         enum : uint64_t { Unselected = std::numeric_limits<uint64_t>::max() - 1 };
         enum class GroupBy : int { Thread, UserText, Callstack };
-        enum class SortBy : int { Order, Count, Time };
+        enum class SortBy : int { Order, Count, Time, Mtpc };
 
         struct Group
         {