improvements when testing leiden

- triple current source
- software loop

cfg/addons/ah2700leiden_cfg.py

@@ -0,0 +1,20 @@
+Node('ah2700.frappy.psi.ch',
+     'Andeen Hagerlin 2700 Capacitance Bridge',
+)
+
+Mod('cap_io',
+    'frappy_psi.ah2700.Ah2700IO',
+    '',
+    uri='linse-leiden-ts:3002',
+    timeout=60,
+)
+
+# this creates also cap_freq and cap_loss
+Mod('cap',
+    'frappy_psi.ah2700.Capacitance',
+    'capacitance',
+    io = 'cap_io',
+    loss_name='loss',
+    freq_name='freq',
+)
+