new syntax for parameter/commands/properties

New Syntax:

- define properties and parameters as class attributes directly
  instead of items in class attribute dicts
- define commands with decorator @usercommand(...)
- old syntax is still supported for now

still to do (with decreasing priority):
- turn parameters into descriptors (vs. creating getters/setters)
- migrate all existing code to new syntax
- get rid of or reduce code in metaclasses using __set_name__ and
  __init_subclass__ instead, including a fix for allowing py < 3.6

Change-Id: Id47e0f89c506f50c40fa518b01822c6e5bbf4e98
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/24991
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/server.py

@@ -244,6 +244,8 @@ class Server:
         for modname, modobj in self.modules.items():
             modobj.initModule()
 
+        if self._testonly:
+            return
         start_events = []
         for modname, modobj in self.modules.items():
             event = threading.Event()