Updated all React components to their latest version

- updated code due to deprecated warnings (mostly router stuff & input default value)
- set default sender based on settings when creating new newsletter
- fixed erroneous UTC offset when displaying dates (PHP takes care of it)

assets/js/src/form/fields/text.jsx

@@ -7,7 +7,10 @@ function(
   var FormFieldText = React.createClass({
     render: function() {
       var value = this.props.item[this.props.field.name];
-      if(!value) { value = null; }
+      if(value === undefined) {
+        value = this.props.field.defaultValue || '';
+      }
+
       return (
         <input
           type="text"
@@ -21,7 +24,6 @@ function(
           id={ 'field_'+this.props.field.name }
           value={ value }
           placeholder={ this.props.field.placeholder }
-          defaultValue={ this.props.field.defaultValue }
           onChange={ this.props.onValueChange }
           {...this.props.field.validation}
         />

assets/js/src/form/form.jsx

@@ -13,10 +13,11 @@ define(
     Router,
     FormField
   ) {
+
     var Form = React.createClass({
-      mixins: [
-        Router.History
-      ],
+      contextTypes: {
+        router: React.PropTypes.object.isRequired
+      },
       getDefaultProps: function() {
         return {
           params: {},
@@ -68,7 +69,7 @@ define(
               loading: false,
               item: {}
             }, function() {
-              this.history.pushState(null, '/new');
+              this.context.router.push('/new');
             }.bind(this));
           } else {
             this.setState({
@@ -118,7 +119,16 @@ define(
             if(this.props.onSuccess !== undefined) {
               this.props.onSuccess();
             } else {
-              this.history.pushState(null, '/')
+              var isChrome = (/Chrome/.test(navigator.userAgent))
+                && (/Google Inc/.test(navigator.vendor));
+              if(
+                (isChrome && history.length > 2)
+                || (!isChrome && history.length > 1)
+              ) {
+                this.context.router.goBack();
+              } else {
+                this.context.router.push('/');
+              }
             }
 
             if(this.props.params.id !== undefined) {