[polari] Add tooltip to room subtitle

[Florian Müllner <fmuellner src gnome org>]

commit 0477a31d7a7a7f08fa0a4d252427d3e7f9d0e2dd
Author: Daniel García Moreno <danigm wadobo com>
Date:   Tue Jan 23 11:33:36 2018 +0100

    Add tooltip to room subtitle
    
    In some rooms the topic is too long and it can't be displayed correctly
    in the titlebar. To view the complete topic I've added a tooltip so if
    you place the mouse over the topic, you can read the full topic.

 data/resources/main-window.ui | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/data/resources/main-window.ui b/data/resources/main-window.ui
index 6fde47e..4056ce8 100644
--- a/data/resources/main-window.ui
+++ b/data/resources/main-window.ui
@@ -125,6 +125,10 @@
                         <property name="use-markup">True</property>
                         <property name="label" bind-source="Gjs_MainWindow"
                                   bind-property="subtitle" bind-flags="sync-create"/>
+                        <property name="has-tooltip" bind-source="Gjs_MainWindow"
+                                  bind-property="subtitle-visible" bind-flags="sync-create" />
+                        <property name="tooltip-markup" bind-source="Gjs_MainWindow"
+                                  bind-property="subtitle" bind-flags="sync-create" />
                         <style>
                           <class name="subtitle"/>
                           <class name="dim-label"/>