fix(tau): do not reserve space for subtitle in headerbar
fixes
<property name="visible">True</property>
<property name="can_focus">False</property>
<property name="title">Tau</property>
+ <property name="has_subtitle">False</property>
<property name="show_close_button">True</property>
<child>
<object class="GtkButton" id="open_button">
