Issue a Token improvements: python, UI fixes, etc.

- Display some errors without marking the step as complete
  (Also applied to Require Destination Tags tutorial)
- Add Python equivalent script

assets/js/tutorials/issue-a-token.js

@@ -174,7 +174,7 @@ $(document).ready(() => {
         "Flags": flags
       }
 
-      generic_full_send(event, cold_settings_tx, cold_secret)
+      await generic_full_send(event, cold_settings_tx, cold_secret)
       complete_step("Configure Issuer")
 
     } catch(err) {
@@ -212,7 +212,7 @@ $(document).ready(() => {
         "Flags": flags
       }
 
-      generic_full_send(event, hot_settings_tx, hot_secret)
+      await generic_full_send(event, hot_settings_tx, hot_secret)
       complete_step("Configure Hot Address")
 
     } catch(err) {
@@ -256,7 +256,7 @@ $(document).ready(() => {
           "value": limit
         }
       }
-      generic_full_send(event, trust_set_tx, hot_secret)
+      await generic_full_send(event, trust_set_tx, hot_secret)
       complete_step("Make Trust Line")
 
     } catch(err) {
@@ -301,7 +301,7 @@ $(document).ready(() => {
       if (use_dest_tag) {
         send_token_tx["DestinationTag"] = dest_tag
       }
-      generic_full_send(event, send_token_tx, cold_secret)
+      await generic_full_send(event, send_token_tx, cold_secret)
       complete_step("Send Token")
 
     } catch(err) {

assets/js/tutorials/require-destination-tags.js

@@ -4,16 +4,21 @@
 $(document).ready(() => {
 
   // 3. Send AccountSet --------------------------------------------------------
-  $("#send-accountset").click( (event) => {
+  $("#send-accountset").click( async (event) => {
     const address = get_address(event)
     if (!address) {return}
 
-    generic_full_send(event, {
-      "TransactionType": "AccountSet",
-      "Account": address,
-      "SetFlag": 1 // RequireDest
-    })
-    complete_step("Send AccountSet")
+    try {
+      await generic_full_send(event, {
+        "TransactionType": "AccountSet",
+        "Account": address,
+        "SetFlag": 1 // RequireDest
+      })
+      complete_step("Send AccountSet")
+    } catch(err) {
+      block.find(".loader").hide()
+      show_error(block, err)
+    }
   })
 
   // 4. Wait for Validation: handled by interactive-tutorial.js and by the