configurables must contain only settable properties

+ bug fix in TCLRequestHandler (decoding error)
+ cosmetic changes

Change-Id: I824e06f1acf975bb59c3312bb97fdfca23e6c975
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21826
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/metaclass.py

@@ -194,10 +194,12 @@ class ModuleMeta(PropertyMeta):
         res = {}
         # collect info about properties
         for pn, pv in cls.properties.items():
-            res[pn] = pv
+            if pv.settable:
+                res[pn] = pv
         # collect info about parameters and their properties
         for param, pobj in cls.accessibles.items():
             res[param] = {}
             for pn, pv in pobj.getProperties().items():
-                res[param][pn] = pv
+                if pv.settable:
+                    res[param][pn] = pv
         return res