Refinement of tech management and MAG reading

- The MAG reader now has access to the details of the proposed
  technology (set in KLayout), specifically inside library paths
  ($(tech_name), $(tech_dir)). This allows setting the MAG reader
  path relative to the technology path.
- If no specific technology is set before MAG files are read and
  the technology listed there is found in KLayout, KLayout will
  attach the layout to this technology.

src/laybasic/laybasic/layCellView.cc

@@ -226,6 +226,9 @@ LayoutHandle::set_tech_name (const std::string &tn)
     } else {
       m_tech_name = std::string ();
     }
+    if (mp_layout) {
+      mp_layout->add_meta_info (db::MetaInfo ("technology", tl::to_string (tr ("Technology name")), tn));
+    }
     technology_changed_event ();
   }
 }