Github Actions, simplify firebase functions and improve python workers performance

Firebase functions

• calculate project progress and project contributorCount in python backend and not with Firebase functions #449
• don't put timestamps in user profile for user contributions

python workers performance

• add logic to generate stats only for recently worked on projects #461
• split backend processing into 3 docker containers for
  a) creation of projects and tutorials
  b) transfer data between firebase and postgres
  c) generate stats and files
• for each docker container the time interval can be set for which jobs should be scheduled
• change logic in update_project_data function to avoid downloading all project information from firebase #459
• using threading in queries for firebase in update_project_data and update_user_data functions #459 #462

Project Creation

• tasks are not uploaded to firebase for build_area, completeness and change detection projects #344

Continuous Integration

• use Github Actions instead of Travis