Split out the local backend (#2052)

This splits the backend into two parts: the local backend for desktop cellxgene and the AWS backend for hosted cellxgene. The local backend is in local_server while the hosted remains in server. The general idea is to copy everything from server to local_server, pull unneeded stuff out of local_server, and keep server as-is for this PR. Not touching server means all the infra and deployment code will continue working just as it did before so we can make those changes incrementally.

local_server/auth/auth_session.py

@@ -0,0 +1,39 @@
+from local_server.auth.auth import AuthTypeBase, AuthTypeFactory
+from flask import session
+from uuid import uuid4
+
+
+class AuthTypeSession(AuthTypeBase):
+    """Session based authentication.  The user is always logged.  The user id is a random number
+    associated with the session.  This is a good choice for desktop servers."""
+
+    # key in the session token for userid
+    CXGUID = "cxguid"
+
+    def __init__(self, app_config):
+        super().__init__()
+
+    def is_valid_authentication_type(self):
+        return True
+
+    def complete_setup(self, app):
+        pass
+
+    def is_user_authenticated(self):
+        # always authenticated
+        return True
+
+    def get_user_id(self):
+        if self.CXGUID not in session:
+            session[self.CXGUID] = uuid4().hex
+            session.permanent = True
+        return session[self.CXGUID]
+
+    def get_user_name(self):
+        return "anonymous"
+
+    def get_user_email(self):
+        return None
+
+
+AuthTypeFactory.register("session", AuthTypeSession)