Set symbol/address prefix to graphene

Change symbol from BTS -> CORE
Change address prefix from BTS -> GPH
These are the graphene values, rather than the bitshares values. The
follow my vote software expects the graphene values.

Also set genesis.json appropriately for follow my vote testing

Author: nathanielhourt

genesis.json

@@ -23,8 +23,8 @@
  */
 #pragma once
 
-#define GRAPHENE_SYMBOL "BTS"
-#define GRAPHENE_ADDRESS_PREFIX "BTS"
+#define GRAPHENE_SYMBOL "CORE"
+#define GRAPHENE_ADDRESS_PREFIX "GPH"
 
 #define GRAPHENE_MIN_ACCOUNT_NAME_LENGTH 1
 #define GRAPHENE_MAX_ACCOUNT_NAME_LENGTH 63