Create event popover: swap buttons' position.

In the create event popover, the Create button is considered to be the right-most button. Because create is a positive action, it seems that it should be the default at the rightmost position.

Swaped create_button and details_button's left_attach arguments.

https://bugzilla.gnome.org/show_bug.cgi?id=747058

data/ui/window.ui

@@ -372,7 +372,7 @@
                 </style>
               </object>
               <packing>
-                <property name="left_attach">0</property>
+                <property name="left_attach">1</property>
                 <property name="top_attach">2</property>
               </packing>
             </child>
@@ -385,7 +385,7 @@
                 <signal name="clicked" handler="create_event" object="GcalWindow" swapped="yes"/>
               </object>
               <packing>
-                <property name="left_attach">1</property>
+                <property name="left_attach">0</property>
                 <property name="top_attach">2</property>
               </packing>
             </child>