dbus: change the JSON timestamp argument to 64 bit

Because we're totally going to ship tuhi in embedded devices that are going to
be in use until after 2038 when time resets to zero, the world goes big bang
and the only survivers will be 64-bit species. Or something like that. Either
way, the API documentation already said so anyway and the DrawingsAvailable
property is already 64 bit too.

Semi-confusingly: the dbus 64 bit unsigned type is 't', it doesn't stand for
'timestamp'.

tools/kete.py

@@ -271,7 +271,7 @@ class TuhiKeteDevice(_DBusObject):
         self.live = False
 
     def json(self, timestamp):
-        return self.proxy.GetJSONData('(u)', timestamp)
+        return self.proxy.GetJSONData('(t)', timestamp)
 
     def _on_signal_received(self, proxy, sender, signal, parameters):
         if signal == 'ButtonPressRequired':

tuhi/dbusserver.py

@@ -87,7 +87,7 @@ INTROSPECTION_XML = '''
     </method>
 
     <method name='GetJSONData'>
-      <arg name='index' type='u' direction='in'/>
+      <arg name='timestamp' type='t' direction='in'/>
       <arg name='json' type='s' direction='out'/>
     </method>