Add version property to all dbus interfaces

data/org.freedesktop.Flatpak.xml

@@ -25,6 +25,7 @@
 
 <node name="/" xmlns:doc="http://www.freedesktop.org/dbus/1.0/doc.dtd">
   <interface name='org.freedesktop.Flatpak.SessionHelper'>
+    <property name="version" type="u" access="read"/>
 
     <method name="RequestMonitor">
       <arg type='ay' name='path' direction='out'/>
@@ -32,6 +33,7 @@
   </interface>
 
   <interface name='org.freedesktop.Flatpak.Development'>
+    <property name="version" type="u" access="read"/>
 
     <!-- This methods let you start processes, sandboxed or not on the
          host, so its not generally safe to allow access to it to any
@@ -59,6 +61,8 @@
   </interface>
 
   <interface name='org.freedesktop.Flatpak.SystemHelper'>
+    <property name="version" type="u" access="read"/>
+
     <method name="Deploy">
       <arg type='ay' name='repo_path' direction='in'/>
       <arg type='u' name='flags' direction='in'/>

data/org.freedesktop.impl.portal.PermissionStore.xml

@@ -42,6 +42,7 @@
       (in the form of a GVariant) with each resource.
   -->
   <interface name='org.freedesktop.impl.portal.PermissionStore'>
+    <property name="version" type="u" access="read"/>
 
     <!--
         Lookup:

data/org.freedesktop.portal.Documents.xml

@@ -47,6 +47,7 @@
       in the POSIX mode bits in the fuse filesystem.
   -->
   <interface name='org.freedesktop.portal.Documents'>
+    <property name="version" type="u" access="read"/>
 
     <!--
         GetMountPoint: