big rework to comply to current spec

- adapt to release(v2018-11-07)
- remove duplicate errors.py
- adapt tests

Change-Id: I383bb571f9808c72b37c12fbe55042011c4c0084
Reviewed-on: https://forge.frm2.tum.de/review/19397
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>

test/test_params.py

@@ -35,10 +35,10 @@ from secop.params import Command, Parameter, Override
 
 
 def test_Command():
-    cmd = Command('do_something', [], None)
+    cmd = Command('do_something')
     assert cmd.description
     assert cmd.ctr
-    assert cmd.arguments == []
+    assert cmd.argument is None
     assert cmd.result is None