Added a better description to cell types

Author: romancardenas

example/celldevs/pandemic_hoya/scenario.json

@@ -34,23 +34,23 @@
         "recovery": 0.4
       }
     },
-    "1": {
+    "epicenter": {
       "state": {
         "population": 100,
         "susceptible": 0.7,
         "infected": 0.3,
         "recovered": 0
       }
     },
-    "2": {
+    "immune": {
       "config": {
         "virulence": 0,
         "recovery": 1
       }
     }
   },
   "cell_map": {
-    "1": [[24, 24]],
-    "2": [[24, 23]]
+    "epicenter": [[24, 24]],
+    "immune": [[24, 23]]
   }
 }