Resolves Bug #U4-5568 Allow 0 for numeric data type

Please see this bug for more detail:
http://issues.umbraco.org/issue/U4-5568

src/Umbraco.Web.UI.Client/src/common/directives/util/fixnumber.directive.js

@@ -24,6 +24,7 @@ function fixNumber($parse) {
 
             //always return an int to the model
             ctrl.$parsers.push(function (value) {
+            	if (value === 0) return 0;
                 return parseFloat(value || '', 10);
             });