implement SECoP proxy modules

A proxy module is a module with a known structure, but
accessed over a SECoP connection.
For the configuration, a Frappy module class has to be given.
The proxy class is created from this, but does not inherit from it.
However, the class of the returned object will be subclass of the
SECoP base classes (Readable, Drivable etc.).
A possible extension might be, that instead of the Frappy class,
the JSON module description can be given, as a separate file
or directly in the config file.
Or we might offer a tool to convert the JSON description to
a python class.

Change-Id: I9212d9f3fe82ec56dfc08611d0e1efc0b0112271
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/22386
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/params.py

@@ -83,10 +83,16 @@ class Parameter(Accessible):
     from the config file if specified there
 
     poll can be:
-    - False or 0 (never poll this parameter), this is the default
-    - True or 1  (poll this parameter)
-    - for any other integer, the meaning depends on the used poller
-      meaning for the default simple poller:
+    - None: will be converted to True/False if handler is/is not None
+    - False or 0 (never poll this parameter)
+    - True or > 0  (poll this parameter)
+    - the exact meaning depends on the used poller
+      meaning for secop.poller.Poller:
+        - 1 or True (AUTO), converted to SLOW (readonly=False), DYNAMIC('status' and 'value') or REGULAR(else)
+        - 2 (SLOW), polled with lower priority and a multiple of pollperiod
+        - 3 (REGULAR), polled with pollperiod
+        - 4 (DYNAMIC), polled with pollperiod, if not BUSY, else with a fraction of pollperiod
+      meaning for the basicPoller:
         - True or 1 (poll this every pollinterval)
         - positive int  (poll every N(th) pollinterval)
         - negative int  (normally poll every N(th) pollinterval, if module is busy, poll every pollinterval)
@@ -110,7 +116,8 @@ class Parameter(Accessible):
                                  ValueType(), export=False, default=None, mandatory=False),
         'export':      Property('Is this parameter accessible via SECoP? (vs. internal parameter)',
                                  OrType(BoolType(), StringType()), export=False, default=True),
-        'poll':        Property('Polling indicator', IntRange(), export=False, default=False),
+        'poll':        Property('Polling indicator', NoneOr(IntRange()), export=False, default=None),
+        'needscfg':    Property('needs value in config', NoneOr(BoolType()), export=False, default=None),
         'optional':    Property('[Internal] is this parameter optional?', BoolType(), export=False,
                                  settable=False, default=False),
         'handler':     Property('[internal] overload the standard read and write functions',
@@ -139,9 +146,6 @@ class Parameter(Accessible):
             datatype.setProperty('unit', unit)
         super(Parameter, self).__init__(**kwds)
 
-        if self.handler and not self.poll:
-            self.properties['poll'] = True
-
         if self.readonly and self.initwrite:
             raise ProgrammingError('can not have both readonly and initwrite!')
 
@@ -182,6 +186,7 @@ class UnusedClass:
     # do not derive anything from this!
     pass
 
+
 class Parameters(OrderedDict):
     """class storage for Parameters"""
     def __init__(self, *args, **kwds):