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/voting/tx.template

@@ -25,7 +25,7 @@
           , [ h'7777777777777777777777777777777777777777777777777777777777777777', 2 ]: [ 2, null ]
 	  }
 
-      , [ 3, h'{{ voting.purposes_vote.hash }}' ]:
+      , [ 3, h'{{ voting.purposes.vote.hash }}' ]:
           { [ h'9999999999999999999999999999999999999999999999999999999999999999', 3 ]: [ 0, null ]
 	  }
 
@@ -33,7 +33,7 @@
           { [ h'9999999999999999999999999999999999999999999999999999999999999999', 4 ]: [ 1, null ]
 	  }
 
-      , [ 1, h'{{ voting.purposes_vote.hash }}' ]:
+      , [ 1, h'{{ voting.purposes.vote.hash }}' ]:
           { [ h'9999999999999999999999999999999999999999999999999999999999999999', 1 ]: [ 1, null ]
 	  }
       }
@@ -43,7 +43,7 @@
 	 , [4, 0, 121([42]), [1000000, 100000000]]
          ]
 
-    , 7: [h'{{ voting.purposes_vote.cbor }}']
+    , 7: [h'{{ voting.purposes.vote.cbor }}']
     },
 
     true,