Use dot to separate purpose from validator name in blueprint

The rationale is two folds:

  1. It's more consistent with how we already separate the validator
  name from its module.

  2. Because `_` may be present in Aiken's validator's name, it is hard
     to read and I am afraid it could potentially conflict later on. So
     it's better to use a separator that cannot appear in validator
     names.

examples/acceptance_tests/script_context/v3/ctx/proposing_pparams/tx.template

@@ -61,7 +61,7 @@
 	      , 32: 20
 	      , 33: 30([15, 1])
 	      }
-	    , h'{{ proposing_pparams.guardrails_propose.hash }}'
+	    , h'{{ proposing_pparams.guardrails.propose.hash }}'
 	    ]
           , [ "https://aiken-lang.org"
             , h'0000000000000000000000000000000000000000000000000000000000000000'
@@ -73,7 +73,7 @@
 
     { 5: [[5, 0, 121([]), [1000000, 100000000]]]
 
-    , 7: [h'{{ proposing_pparams.guardrails_propose.cbor }}']
+    , 7: [h'{{ proposing_pparams.guardrails.propose.cbor }}']
     },
 
     true,