support write_ method on readonly param and more

- write method may be used internally on a readonly parameter
+ add IDLE, WARN, BUSY and ERROR to secop.core
+ secop.datatype.EnumType: allow 'self' as member name
+ secop.lib.statemachine: log Restart and Stop exceptions only on debug level
+ secop_psi.ccu4.CCU4: explicit conversion to float
+ secop.proxy: remove superfluos and erroneous make_secop_error

Change-Id: I2f13d31ceacd2bde65eab64f8eae4225556c18f5
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/27963
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_lib_enum.py

@@ -64,6 +64,7 @@ def test_EnumMember():
     assert a != 3
     assert a == 1
 
+
 def test_Enum():
     e1 = Enum('e1')
     e2 = Enum('e2', e1, a=1, b=3)
@@ -75,3 +76,4 @@ def test_Enum():
     assert e2.b > e3.a
     assert e3.c >= e2.a
     assert e3.b <= e2.b
+    assert Enum({'self': 0, 'other': 1})('self') == 0