Add number of units to the delay node (rate) (#994)

* Add possibility to set the value for the rate unit

Backward compatible, if the new nbRateUnits is not set, default to 1.
This way we can delay messages to 1 msg per X seconds/minutes/hours days
instead of always 1.
Useful when interacting with API that have a uncommon rate limiting like
1req per 2 seconds.

* Fix existing testing for delay

* Add new test for the nbRateUnits

* Fix label for timed and topic for delay node

* Schrink width of Units delay rate

* pluralisation of labels

* Dynamic pluralisation respecting i18n

* Remove debug data left

nodes/core/locales/en-US/messages.json

@@ -200,7 +200,25 @@
             "limit": "limit",
             "random": "random",
             "queue": "queue",
-            "timed": "releases per"
+            "timed": "releases per",
+            "units" : {
+                "second": {
+                    "plural" : "Seconds",
+                    "singular": "Second"
+                },
+                "minute": {
+                    "plural" : "Minutes",
+                    "singular": "Minute"
+                },
+                "hour": {
+                    "plural" : "Hours",
+                    "singular": "Hour"
+                },
+                "day": {
+                    "plural" : "Days",
+                    "singular": "Day"
+                }
+            }
         },
         "error": {
             "buffer": "buffer exceeded 1000 messages",