move historywriter to secop_psi

as historywriter currently could be used at psi only
secop_psi is a better place for it

+ add comment about a general config file

Change-Id: I9b0e74d3da83ac485bd4bcc13475695c3140822c
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/25077
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/lib/__init__.py

@@ -52,9 +52,12 @@ else:
 # overwrite with env variables SECOP_LOGDIR, SECOP_PIDDIR, SECOP_CONFDIR, if present
 for dirname in CONFIG:
     CONFIG[dirname] = environ.get('SECOP_%s' % dirname.upper(), CONFIG[dirname])
+
 # this is not customizable
 CONFIG['basedir'] = repodir
 
+# TODO: if ever more general options are need, we should think about a general config file
+
 
 unset_value = object()