server: Add address index to transaction_inputs and transaction_outputs

This is useful to retrieve transactions by address from the database,
part of #18.

server/conf/evolutions/default/6.sql

@@ -0,0 +1,13 @@
+
+# --- !Ups
+
+CREATE INDEX transaction_inputs_address_index ON transaction_inputs (address);
+
+CREATE INDEX transaction_outputs_address_index ON transaction_outputs (address);
+
+
+# --- !Downs
+
+DROP INDEX transaction_outputs_address_index;
+
+DROP INDEX transaction_inputs_address_index;