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>

test/test_params.py

@@ -57,7 +57,7 @@ def test_Parameter():
     assert p1 != p2
     assert p1.ctr != p2.ctr
     with pytest.raises(ProgrammingError):
-        Parameter(None, datatype=float)
+        Parameter(None, datatype=float, inherit=False)
     p3 = p1.copy()
     assert p1.ctr == p3.ctr
     p3.ctr = p1.ctr # manipulate ctr for next line