Backend cleanup

[pheonix8]

• updated tests:

  • clean test structure
  • remove unneccesary test (auth error)
  • add tests for 500 error No DB
  • added root endpoint test

• updated endpoints:

  • removed /api now handled via root_path (dockerfile)
  • standardised enpoints to /plans
  • added try except to plan endpoints

• updated database:

  • added sqlalchemie sessionmaker
  • cleaned get_session function

• updated linting:

  • removed F401 from linting exceptions
  • # noqa: F401 can be used to exclude lines like in create_tables.py