server: add option to dynamically create devices

add module which scans a connection and registers new devices depending
on the answer.
* change module initialization to demand-based
* move code from server to dispatcher
- remove intermediate step in Attached __get__

TODO:
  factor out dispatcher (regards to playground)
  discuss factoring out of module creation code from server AND
  dispatcher

Change-Id: I7af959b99a84c291c526aac067a4e2bf3cd741d4
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/31470
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Georg Brandl <g.brandl@fz-juelich.de>
Reviewed-by: Alexander Zaft <a.zaft@fz-juelich.de>

frappy_demo/test.py

@@ -24,10 +24,33 @@
 import random
 
 from frappy.datatypes import FloatRange, StringType, ValueType, TupleOf, StructOf, ArrayOf
-from frappy.modules import Communicator, Drivable, Parameter, Property, Readable, Module
+from frappy.modules import Communicator, Drivable, Parameter, Property, Readable, Module, Attached
 from frappy.params import Command
+from frappy.dynamic import Pinata
 from frappy.errors import RangeError
 
+class Pin(Pinata):
+    def scanModules(self):
+        yield ('pin_a', {'cls': LN2, 'description':'hi'})
+        yield ('pin_b', {'cls': LN2, 'description':'hi'})
+
+class RecPin(Pinata):
+    def scanModules(self):
+        yield ('rec_a', {'cls': RecPinInner, 'description':'hi'})
+        yield ('rec_b', {'cls': RecPinInner, 'description':'hi'})#, 'idx':'_2'})
+
+class RecPinInner(Pinata):
+    idx = Property('', StringType(), default='')
+    def scanModules(self):
+        yield ('pin_pin_a' + self.idx, {'cls': Mapped, 'description':'recursive!', 'choices':['A', 'B']})
+        yield ('pin_pin_b' + self.idx, {'cls': Mapped, 'description':'recursive!', 'choices':['A', 'B']})
+
+
+class WithAtt(Readable):
+    att = Attached()
+
+    def read_value(self):
+        return self.att.read_value()
 
 class LN2(Readable):
     """Just a readable.