Backend fix login

Fixes issue #1 (closed)

Summary of changes

• UserAccount entity type added to datastore
• User's email address is checked against the database and user entity with the user's assigned roles is added to the session instead of the google account
• Created custom error AuthenticationError and moved all custom errors to a single module
• Added better exception handling and logging to the login process

changed the description

added 1 commit

• 32867776 - Update datastore.py

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merged

mentioned in commit 90742478