feat(config): basis for simplified value setting

Previously we would set static structures manully, using complex cases
and utility functions. Now we setup the foundation to allow setting
a generic `json::value::Value` instead, which can later be deserialized
into the target structure.

Related to #111

src/rust/cli/cmn.rs

@@ -199,6 +199,10 @@ impl FieldCursor {
         }
     }
 
+    pub fn set_json_value(&self, object: &mut json::value::Value, value: &str, value_type: &str) {
+        
+    }
+
     pub fn num_fields(&self) -> usize {
         self.0.len()
     }