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/core.py

@@ -31,7 +31,7 @@ from secop.datatypes import FloatRange, IntRange, ScaledInteger, \
 from secop.lib.enum import Enum
 from secop.modules import Module, Readable, Writable, Drivable, Communicator, Attached
 from secop.properties import Property
-from secop.params import Parameter, Command, Override
+from secop.params import Parameter, Command, Override, usercommand
 from secop.metaclass import Done
 from secop.iohandler import IOHandler, IOHandlerBase
 from secop.stringio import StringIO, HasIodev