window: block automatic creation of nameless events

We shouldn't let nameless events be created.
This commit blocks all ways to create them
when the name is not set.

The user can still edit events' data.

data/ui/window.ui

@@ -367,6 +367,7 @@
                 <property name="visible">True</property>
                 <property name="can_focus">True</property>
                 <property name="receives_default">True</property>
+                <property name="sensitive">False</property>
                 <signal name="clicked" handler="create_event" object="GcalWindow" swapped="yes"/>
                 <style>
                   <class name="suggested-action"/>
@@ -396,6 +397,7 @@
                 <property name="can_focus">True</property>
                 <property name="hexpand">True</property>
                 <signal name="activate" handler="create_event" object="GcalWindow" swapped="yes"/>
+                <signal name="notify::text" handler="new_event_entry_text_changed" object="GcalWindow" swapped="yes"/>
               </object>
               <packing>
                 <property name="left_attach">0</property>