db.Session: Add

Add database session API to db. This is a breaking change, because
from this commit on, a session object has to be passed to every
query.

This commit also removes any reference to Cmds / App objects. An
instantiated database object can be worked with outside of an App.

Signed-off-by: Jan Lindemann <jan@janware.com>

tools/python/jwutils/db/Session.py

@@ -0,0 +1,12 @@
+# -*- coding: utf-8 -*-
+
+import abc
+
+class Session(abc.ABC): # export
+
+    def __init__(self, db):
+        self.__db = db
+
+    @property
+    def db(self):
+        return self.__db