[gnome-calendar] edit-dialog: improve titlebar button

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 5cb2e86fa620269cab6df6a9a28925405686e8ce
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Wed Jul 6 18:45:39 2016 -0300

    edit-dialog: improve titlebar button
    
    Make it insensitive when the event is read-only, and add
    a tooltip for users to learn what does the button do.

 data/ui/edit-dialog.ui |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/data/ui/edit-dialog.ui b/data/ui/edit-dialog.ui
index ec597f9..8135a57 100644
--- a/data/ui/edit-dialog.ui
+++ b/data/ui/edit-dialog.ui
@@ -36,6 +36,8 @@
             <property name="can_focus">True</property>
             <property name="receives_default">True</property>
             <property name="popover">sources_popover</property>
+            <property name="sensitive" bind-source="GcalEditDialog" bind-property="writable" 
bind-flags="default" />
+            <property name="tooltip-text" translatable="yes">Click to select the event's agenda</property>
             <style>
               <class name="flat"/>
               <class name="sources-button"/>