add aurweb.models.session.Session ORM database object

+ Added aurweb.util module.
    - Added make_random_string function.
+ Added aurweb.db.make_random_value function.
    - Takes a model and a column and introspects them to figure out the
      proper column length to create a random string for; then creates
      a unique string for that column.

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/models/session.py

@@ -0,0 +1,25 @@
+from sqlalchemy import Column, Integer
+from sqlalchemy.orm import backref, mapper, relationship
+
+from aurweb.db import make_random_value
+from aurweb.models.user import User
+from aurweb.schema import Sessions
+
+
+class Session:
+    UsersID = Column(Integer, nullable=True)
+
+    def __init__(self, **kwargs):
+        self.UsersID = kwargs.get("UsersID")
+        self.SessionID = kwargs.get("SessionID")
+        self.LastUpdateTS = kwargs.get("LastUpdateTS")
+
+
+mapper(Session, Sessions, primary_key=[Sessions.c.SessionID], properties={
+    "User": relationship(User, backref=backref("session",
+                                               uselist=False))
+})
+
+
+def generate_unique_sid():
+    return make_random_value(Session, Session.SessionID)