Update and (almost) completing Dutch strings for 1.5 (#4351)

* Update and expanding Dutch strings for 1.5

Only privacy policy is not translated, but is included. Hopefully I have time to translate this another time (you can set your own privacy policy now anyway).

* Missing file

* A few changes cause of changes in another file

* Fix

* Update Dutch strings for 1.5

* nl

* fix

don't know how that ended up there

* Update nl.yml

config/locales/activerecord.nl.yml

@@ -0,0 +1,12 @@
+nl:
+  activerecord:
+    errors:
+      models:
+        account:
+          attributes:
+            username:
+              invalid: alleen letters, nummers en underscores
+        status:
+          attributes:
+            reblog:
+              taken: van toot bestaat al